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Practice › LeetCode › LeetCode 38xx ›

LeetCode 3831 - Median of a Binary Search Tree Level

LeetCode Problem 3831 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Breadth-First Search, Binary Search Tree, Binary Tree Solution Corrected Solution for Exercise 4.3.1.9 Exercise 4.3.1.9 asks for a generalization of Algorithm A to add two $n$-place numbers in a mixed-radix system with bases $b_0, b_1, \dots, b_{n-1}$ from right to left. Algorithm A in TAOCP §4.3.1 describes standard addition with carry propagation in a single-radix positional system. Here we adapt...

Practice › LeetCode › LeetCode 35xx ›

LeetCode 3526 - Range XOR Queries with Subarray Reversals

LeetCode Problem 3526 Difficulty: 🔴 Hard Topics: Array, Tree, Binary Tree Solution Here’s a full technical solution guide for LeetCode 3526 - Range XOR Queries with Subarray Reversals following your requested structure and formatting: Problem Understanding The problem provides an array nums of integers and a list of queries , where each query can either update a value in the array, reverse a subarray, or compute the XOR of a...

Practice › LeetCode › LeetCode 38xx ›

LeetCode 3879 - Maximum Distinct Path Sum in a Binary Tree

LeetCode Problem 3879 Difficulty: 🟡 Medium Topics: Hash Table, Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to find the maximum sum of node values along a path in a binary tree such that all values in the path are distinct . The path can start and end at any node, does not need to pass through the root, and must consist of connected nodes. Each...

Practice › LeetCode › LeetCode 25xx ›

LeetCode 2509 - Cycle Length Queries in a Tree

LeetCode Problem 2509 Difficulty: 🔴 Hard Topics: Array, Tree, Binary Tree Solution Problem Understanding The problem gives us a complete binary tree where nodes are labeled in the same way as a binary heap. For every node with value x : Its left child is 2 * x Its right child is 2 * x + 1 The tree contains all node values from 1 to 2^n - 1 ....

Practice › LeetCode › LeetCode 24xx ›

LeetCode 2458 - Height of Binary Tree After Subtree Removal Queries

LeetCode Problem 2458 Difficulty: 🔴 Hard Topics: Array, Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding This problem asks us to answer multiple independent queries on a binary tree. For each query, we temporarily remove an entire subtree rooted at a specific node, then compute the height of the remaining tree. The binary tree contains n nodes, and every node has a unique value from 1 to n...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2049 - Count Nodes With the Highest Score

LeetCode Problem 2049 Difficulty: 🟡 Medium Topics: Array, Tree, Depth-First Search, Binary Tree Solution Problem Understanding The input describes a rooted binary tree using a parent array. Every node is identified by an integer from 0 to n - 1 , and parents[i] tells us which node is the parent of node i . The root node is always 0 , so its parent is -1 . The goal is...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2792 - Count Nodes That Are Great Enough

LeetCode Problem 2792 Difficulty: 🔴 Hard Topics: Divide and Conquer, Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem gives us the root of a binary tree and an integer k . We must determine how many nodes in the tree are considered "great enough". A node is great enough if two conditions are satisfied: Its subtree contains at least k nodes. Its value is greater than the values...

Practice › LeetCode › LeetCode 24xx ›

LeetCode 2471 - Minimum Number of Operations to Sort a Binary Tree by Level

LeetCode Problem 2471 Difficulty: 🟡 Medium Topics: Tree, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to determine the minimum number of swap operations required to sort the values of a binary tree level by level in strictly increasing order. Specifically, at each level of the tree, we can only swap values of nodes that exist on that level. The tree is given as a standard binary...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2773 - Height of Special Binary Tree

LeetCode Problem 2773 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution LeetCode 2773 - Height of Special Binary Tree Problem Understanding This problem gives us the root of a special binary tree. At first glance, it looks like a normal binary tree, but there is an unusual property involving the leaf nodes. Suppose the leaves of the tree, ordered by their node values, are: $$b_1 <...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2313 - Minimum Flips in Binary Tree to Get Result

LeetCode Problem 2313 Difficulty: 🔴 Hard Topics: Dynamic Programming, Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem presents a binary tree where leaf nodes represent boolean values 0 (false) or 1 (true), and internal nodes represent boolean operations OR , AND , XOR , and NOT , encoded as integers 2 , 3 , 4 , and 5 . You are also given a target boolean result. The...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2096 - Step-By-Step Directions From a Binary Tree Node to Another

LeetCode Problem 2096 Difficulty: 🟡 Medium Topics: String, Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem gives us a binary tree where every node contains a unique value from 1 to n . We are also given two node values: startValue , the node where the path begins destValue , the node where the path must end We must return the shortest sequence of directions needed to move...

Practice › LeetCode › LeetCode 33xx ›

LeetCode 3319 - K-th Largest Perfect Subtree Size in Binary Tree

LeetCode Problem 3319 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Sorting, Binary Tree Solution LeetCode 3319 - K-th Largest Perfect Subtree Size in Binary Tree Problem Understanding We are given the root of a binary tree and an integer k . Our goal is to find the size of the k -th largest perfect binary subtree contained anywhere within the tree. A perfect binary tree has two defining properties: Every...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2331 - Evaluate Boolean Binary Tree

LeetCode Problem 2331 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to evaluate a full binary tree where each node represents either a boolean value or a boolean operation. Leaf nodes have values 0 (False) or 1 (True). Non-leaf nodes have values 2 (OR) or 3 (AND). The goal is to compute the boolean value at the root by recursively evaluating all...

Practice › LeetCode › LeetCode 24xx ›

LeetCode 2415 - Reverse Odd Levels of Binary Tree

LeetCode Problem 2415 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to reverse the values of nodes at odd levels of a perfect binary tree . A perfect binary tree is a tree in which every parent node has exactly two children and all leaves appear at the same depth. The root node is at level 0 (even), its children...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1932 - Merge BSTs to Create Single BST

LeetCode Problem 1932 Difficulty: 🔴 Hard Topics: Array, Hash Table, Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding This problem asks us to take multiple very small binary search trees (BSTs), each with at most three nodes, and attempt to merge them into a single valid BST. Each tree is represented by its root node in the array trees . The only operation allowed is to attach...

Practice › LeetCode › LeetCode 25xx ›

LeetCode 2583 - Kth Largest Sum in a Binary Tree

LeetCode Problem 2583 Difficulty: 🟡 Medium Topics: Tree, Breadth-First Search, Sorting, Binary Tree Solution Problem Understanding The problem gives us the root of a binary tree and an integer k . For every level in the tree, we calculate the sum of all node values that appear on that level. After computing all level sums, we must return the kth largest level sum. A binary tree level is determined by...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2689 - Extract Kth Character From The Rope Tree

LeetCode Problem 2689 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Tree Solution Edit LeetCode 2689 - Extract Kth Character From The Rope Tree Problem Understanding This problem asks us to retrieve the k-th character from a string represented by a special binary tree called a rope tree . Instead of storing one large string directly, the string is distributed across the tree structure. Each node in the tree belongs...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2265 - Count Nodes Equal to Average of Subtree

LeetCode Problem 2265 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to count how many nodes in a binary tree satisfy a specific condition: the node’s value must equal the average value of all nodes in its subtree . A subtree consists of the current node and every descendant below it. For each node, we need to compute: The total sum of...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2641 - Cousins in Binary Tree II

LeetCode Problem 2641 Difficulty: 🟡 Medium Topics: Hash Table, Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem gives us the root of a binary tree and asks us to replace every node’s value with the sum of all of its cousins’ values. Two nodes are considered cousins if: They are at the same depth in the tree They do not share the same parent The depth...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2764 - Is Array a Preorder of Some ‌Binary Tree

LeetCode Problem 2764 Difficulty: 🟡 Medium Topics: Stack, Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to determine whether a given list of nodes represents the preorder traversal of a binary tree. Each node is represented as a pair [id, parentId] , where id is the unique identifier of the node, and parentId identifies its parent in the tree. A parentId of -1 indicates that the...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2385 - Amount of Time for Binary Tree to Be Infected

LeetCode Problem 2385 Difficulty: 🟡 Medium Topics: Hash Table, Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding This problem asks us to model the spread of an infection across a binary tree. Each node in the tree has a unique integer value, and the infection starts from a specific node, identified by start . The infection spreads to adjacent nodes-this means both the parent and child nodes of...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2196 - Create Binary Tree From Descriptions

LeetCode Problem 2196 Difficulty: 🟡 Medium Topics: Array, Hash Table, Tree, Binary Tree Solution Problem Understanding The problem asks us to construct a binary tree from a list of relationships, where each relationship is given as [parent, child, isLeft] . Here, parent is the value of a node, child is the value of its direct descendant, and isLeft indicates whether child is a left child ( 1 ) or a...

Practice › LeetCode › LeetCode 24xx ›

LeetCode 2445 - Number of Nodes With Value One

LeetCode Problem 2445 Difficulty: 🟡 Medium Topics: Array, Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The tree in this problem is not given explicitly through an edge list. Instead, the structure is defined mathematically. Every node v has parent floor(v / 2) , which creates the same structure as a binary heap. For example: Node 2 and node 3 are children of node 1 Node 4 and...

Practice › LeetCode › LeetCode 31xx ›

LeetCode 3157 - Find the Level of Tree with Minimum Sum

LeetCode Problem 3157 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem gives us the root of a binary tree, where every node contains a positive integer value. Our task is to determine which level of the tree has the smallest sum of node values. A binary tree is organized into levels: The root node is at level 1 Its children are at...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1902 - Depth of BST Given Insertion Order

LeetCode Problem 1902 Difficulty: 🟡 Medium Topics: Array, Tree, Binary Search Tree, Binary Tree, Ordered Set Solution Problem Understanding The problem gives us an array order that represents the exact sequence in which values are inserted into a binary search tree, usually abbreviated as BST. The array is a permutation of integers from 1 to n , which means every value appears exactly once and there are no duplicates. We...

Practice › LeetCode › LeetCode 24xx ›

LeetCode 2476 - Closest Nodes Queries in a Binary Search Tree

LeetCode Problem 2476 Difficulty: 🟡 Medium Topics: Array, Binary Search, Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding The problem gives us the root of a binary search tree, abbreviated as BST, along with a list of query values. For every query, we must determine two numbers: The largest value in the BST that is less than or equal to the query. The smallest value in the...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1973 - Count Nodes Equal to Sum of Descendants

LeetCode Problem 1973 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to analyze a binary tree and count how many nodes satisfy a specific property: the value of the node equals the sum of all its descendants. A descendant of a node is any node that lies in the subtree rooted at that node excluding the node itself. For example, if a...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2673 - Make Costs of Paths Equal in a Binary Tree

LeetCode Problem 2673 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Greedy, Tree, Binary Tree Solution Edit LeetCode 2673 - Make Costs of Paths Equal in a Binary Tree Problem Understanding This problem gives us a perfect binary tree with n nodes, where each node has an associated cost. The tree follows a strict indexing rule: node i has a left child at 2 * i and a right child at...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2236 - Root Equals Sum of Children

LeetCode Problem 2236 Difficulty: 🟢 Easy Topics: Tree, Binary Tree Solution Problem Understanding This problem gives us a binary tree that always contains exactly three nodes. There is one root node, one left child, and one right child. We must determine whether the value stored in the root node is equal to the sum of the values stored in its two children. In other words, if: root.val is the value...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 101 - Symmetric Tree

LeetCode Problem 101 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to determine whether a binary tree is symmetric around its center. A tree is symmetric if the left subtree is a mirror reflection of the right subtree. In a mirror relationship, the following conditions must hold: The values of the corresponding nodes must be equal. The left child of...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 144 - Binary Tree Preorder Traversal

LeetCode Problem 144 Difficulty: 🟢 Easy Topics: Stack, Tree, Depth-First Search, Binary Tree Solution LeetCode 144, Binary Tree Preorder Traversal Problem Understanding This problem asks us to return the preorder traversal of a binary tree. A binary tree consists of nodes where each node may have a left child and a right child. The input root represents the root node of that tree. In a preorder traversal, nodes are visited...

Practice › LeetCode › LeetCode 03xx ›

LeetCode 331 - Verify Preorder Serialization of a Binary Tree

LeetCode Problem 331 Difficulty: 🟡 Medium Topics: String, Stack, Tree, Binary Tree Solution Problem Understanding The problem gives us a string that represents the preorder serialization of a binary tree. Each value is separated by commas. A normal integer represents a real tree node, while the character '#' represents a null pointer. In preorder traversal, we always visit nodes in this order: Current node Left subtree Right subtree For example,...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 107 - Binary Tree Level Order Traversal II

LeetCode Problem 107 Difficulty: 🟡 Medium Topics: Tree, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to traverse a binary tree and return the node values level by level, but in bottom-up order . Normally, a level order traversal collects values from the root down to the leaves. Here, we need to reverse that order and return the leaf levels first, moving up to the root. The...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 117 - Populating Next Right Pointers in Each Node II

LeetCode Problem 117 Difficulty: 🟡 Medium Topics: Linked List, Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to populate the next pointer for every node in a binary tree so that it points to the node immediately to its right on the same level. If no such node exists, the next pointer should remain NULL . Unlike the easier version of this problem, where...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1302 - Deepest Leaves Sum

LeetCode Problem 1302 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution That is a long, comprehensive reference document with multiple sections and full code in two languages. To keep quality high and avoid truncation, I should provide it in a canvas document. I’ll include all requested sections in one complete guide: Problem Understanding Approaches (brute force and optimal) Comparison table Algorithm Walkthrough with proof sketch Complete...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 897 - Increasing Order Search Tree

LeetCode Problem 897 Difficulty: 🟢 Easy Topics: Stack, Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding This problem gives us the root of a Binary Search Tree, abbreviated as BST, and asks us to rearrange the tree into a very specific form. A Binary Search Tree has the property that for every node: All values in the left subtree are smaller All values in the right subtree...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 145 - Binary Tree Postorder Traversal

LeetCode Problem 145 Difficulty: 🟢 Easy Topics: Stack, Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to return the postorder traversal of a binary tree. A binary tree is made of nodes, where each node contains: A value A pointer to a left child A pointer to a right child In postorder traversal, we must visit nodes in this exact order: Traverse the left subtree Traverse...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 404 - Sum of Left Leaves

LeetCode Problem 404 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem gives us the root node of a binary tree and asks us to compute the sum of all left leaves in the tree. A binary tree node may have up to two children, a left child and a right child. A leaf node is a node that has no children at...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 958 - Check Completeness of a Binary Tree

LeetCode Problem 958 Difficulty: 🟡 Medium Topics: Tree, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to determine whether a given binary tree is a complete binary tree . A complete binary tree has a specific structural property: every level, except possibly the last, is completely filled, and in the last level, all nodes appear as far left as possible. The input is the root of a...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1026 - Maximum Difference Between Node and Ancestor

LeetCode Problem 1026 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to find the largest absolute difference between the values of two nodes in a binary tree, under one important condition: one node must be an ancestor of the other. In a binary tree, an ancestor of a node is any node that appears on the path from the root down to...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1485 - Clone Binary Tree With Random Pointer

LeetCode Problem 1485 Difficulty: 🟡 Medium Topics: Hash Table, Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution That’s a detailed reference guide with multiple required sections and full implementations. Before I start, please confirm one detail: Do you want the complete guide for LeetCode 1485 in a single response , including all sections (Problem Understanding, Approaches, Algorithm Walkthrough, Python Solution, Go Solution, Worked Examples, Complexity Analysis, Test Cases, and Edge...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1612 - Check If Two Expression Trees are Equivalent

LeetCode Problem 1612 Difficulty: 🟡 Medium Topics: Hash Table, Tree, Depth-First Search, Binary Tree, Counting Solution Problem Understanding The problem asks us to determine whether two binary expression trees are equivalent, where equivalence is defined as the trees representing the same arithmetic expression, modulo the order of addition since addition is commutative. Each tree node contains either a '+' operator (for internal nodes) or a variable (for leaf nodes). The...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 971 - Flip Binary Tree To Match Preorder Traversal

LeetCode Problem 971 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to manipulate a binary tree so that its pre-order traversal matches a given sequence called voyage . In other words, we are given a tree and a list of integers, and we want to see if we can transform the tree by flipping nodes (swapping their left and right children) so...

Practice › LeetCode › LeetCode 03xx ›

LeetCode 366 - Find Leaves of Binary Tree

LeetCode Problem 366 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to repeatedly remove all leaf nodes from a binary tree and record the values removed during each round. A leaf node is a node with no left or right child. During each iteration, we collect every current leaf node, remove them conceptually from the tree, and continue the process until the...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 100 - Same Tree

LeetCode Problem 100 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to determine whether two binary trees are exactly the same. We are given the roots of two binary trees, p and q . A binary tree consists of nodes where each node contains a value and references to a left child and a right child. The task is to...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 250 - Count Univalue Subtrees

LeetCode Problem 250 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to count how many subtrees in a binary tree are "uni-value" subtrees. A uni-value subtree is a subtree in which every node has the same value. A subtree consists of a node together with all of its descendants. This means every node in the tree can potentially serve as the root...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1530 - Number of Good Leaf Nodes Pairs

LeetCode Problem 1530 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution LeetCode 1530 - Number of Good Leaf Nodes Pairs Problem Understanding This problem gives us the root of a binary tree and an integer distance . We need to count how many pairs of leaf nodes satisfy a specific condition: the shortest path between the two leaves must be less than or equal to distance . A...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 617 - Merge Two Binary Trees

LeetCode Problem 617 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding This problem asks us to combine two binary trees into a single merged tree. Each tree consists of nodes where every node contains a value and pointers to a left and right child. The merge process starts from the roots of both trees and proceeds recursively through corresponding positions in the trees. Whenever...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 450 - Delete Node in a BST

LeetCode Problem 450 Difficulty: 🟡 Medium Topics: Tree, Binary Search Tree, Binary Tree Solution Problem Understanding The problem asks us to delete a node with a specific value, key , from a Binary Search Tree, abbreviated as BST, and return the possibly updated root of the tree. A Binary Search Tree has an important ordering property: Every node in the left subtree contains a value smaller than the current node....

Practice › LeetCode › LeetCode 09xx ›

LeetCode 938 - Range Sum of BST

LeetCode Problem 938 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding This problem gives us the root of a Binary Search Tree, abbreviated as BST, along with two integers, low and high . We must compute the sum of all node values whose values lie inside the inclusive range [low, high] . A Binary Search Tree has an important property: Every node in...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 652 - Find Duplicate Subtrees

LeetCode Problem 652 Difficulty: 🟡 Medium Topics: Hash Table, Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem gives us the root of a binary tree and asks us to identify all duplicate subtrees inside it. A subtree is defined as any node together with all of its descendants. Two subtrees are considered duplicates if they have exactly the same structure and every corresponding node contains the same value....

Practice › LeetCode › LeetCode 04xx ›

LeetCode 426 - Convert Binary Search Tree to Sorted Doubly Linked List

LeetCode Problem 426 Difficulty: 🟡 Medium Topics: Linked List, Stack, Tree, Depth-First Search, Binary Search Tree, Binary Tree, Doubly-Linked List Solution Problem Understanding The problem asks us to transform a Binary Search Tree, abbreviated as BST, into a sorted circular doubly linked list. The transformation must happen in place, meaning we are not allowed to create entirely new nodes for the linked list. Instead, we reuse the existing tree nodes...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 98 - Validate Binary Search Tree

LeetCode Problem 98 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding This problem asks us to determine whether a given binary tree satisfies the rules of a Binary Search Tree, commonly abbreviated as BST. A binary tree consists of nodes where each node contains a value and pointers to a left child and a right child. In a BST, every node must follow...

Practice › LeetCode › LeetCode 03xx ›

LeetCode 314 - Binary Tree Vertical Order Traversal

LeetCode Problem 314 Difficulty: 🟡 Medium Topics: Hash Table, Tree, Depth-First Search, Breadth-First Search, Sorting, Binary Tree Solution Problem Understanding The problem asks us to group the nodes of a binary tree by their vertical columns and return those groups from left to right. Each node in the tree belongs to a conceptual coordinate system: The root starts at column 0 Moving to the left child decreases the column index...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 606 - Construct String from Binary Tree

LeetCode Problem 606 Difficulty: 🟡 Medium Topics: String, Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to convert a binary tree into a string using a very specific preorder traversal format. We must visit nodes in the order root → left subtree → right subtree , and represent the structure of the tree using parentheses. Each node contributes its integer value to the final string. If...

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LeetCode 536 - Construct Binary Tree from String

LeetCode Problem 536 Difficulty: 🟡 Medium Topics: String, Stack, Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to reconstruct a binary tree from a specially formatted string representation. The input string contains integer values and parentheses. Every integer represents a tree node, and parentheses represent child subtrees. The structure follows a recursive pattern: A node value appears first. If the node has children, they are enclosed...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 666 - Path Sum IV

LeetCode Problem 666 Difficulty: 🟡 Medium Topics: Array, Hash Table, Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem encodes a binary tree into a compact array of three-digit integers. Each integer stores three pieces of information: The hundreds digit represents the depth of the node. The tens digit represents the node's position within that depth level. The units digit represents the node's actual value. For example, the integer...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1028 - Recover a Tree From Preorder Traversal

LeetCode Problem 1028 Difficulty: 🔴 Hard Topics: String, Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem provides a string traversal representing a preorder depth-first traversal of a binary tree, where each node is represented by its value preceded by D dashes, with D being the depth of the node in the tree. The root node has depth 0 and is not preceded by any dash. If a node...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1740 - Find Distance in a Binary Tree

LeetCode Problem 1740 Difficulty: 🟡 Medium Topics: Hash Table, Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding This problem asks us to determine the distance between two nodes in a binary tree, given their values p and q . The distance is defined as the number of edges in the shortest path connecting the two nodes. The input is the root of a binary tree and two integers...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1469 - Find All The Lonely Nodes

LeetCode Problem 1469 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding This problem asks us to traverse a binary tree and identify every node that is considered "lonely". A node is lonely if it is the only child of its parent. In other words, if a parent node has exactly one child, that child is lonely. The input is the root of a binary...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 230 - Kth Smallest Element in a BST

LeetCode Problem 230 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding This problem gives us the root of a Binary Search Tree, abbreviated as BST, along with an integer k . We need to return the kth smallest value in the tree. A Binary Search Tree has a very important property: Every value in the left subtree is smaller than the current node....

Practice › LeetCode › LeetCode 06xx ›

LeetCode 655 - Print Binary Tree

LeetCode Problem 655 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to transform a binary tree into a formatted 2D string matrix representation. Each node must appear in a specific row and column based on its position in the tree. The output is not simply a traversal order, it is a visual layout of the tree structure. We are given...

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LeetCode 1110 - Delete Nodes And Return Forest

LeetCode Problem 1110 Difficulty: 🟡 Medium Topics: Array, Hash Table, Tree, Depth-First Search, Binary Tree Solution LeetCode 1110 - Delete Nodes And Return Forest Problem Understanding This problem gives us the root of a binary tree and a list of node values that must be deleted from the tree. Every node value in the tree is unique, which is important because it means we can identify nodes directly by value...

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LeetCode 1315 - Sum of Nodes with Even-Valued Grandparent

LeetCode Problem 1315 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution That is a long, structured reference document and will exceed a single response comfortably. I can provide the complete guide in the exact format you requested. Before I start, one quick clarification: do you want the full solution guide for LeetCode 1315 - Sum of Nodes with Even-Valued Grandparent , including Problem Understanding, Approaches, Algorithm...

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LeetCode 124 - Binary Tree Maximum Path Sum

LeetCode Problem 124 Difficulty: 🔴 Hard Topics: Dynamic Programming, Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem is asking us to find the maximum path sum in a binary tree. A path is defined as any sequence of nodes connected by edges, where each node is included at most once . The path does not need to start at the root or end at a leaf. The sum...

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LeetCode 104 - Maximum Depth of Binary Tree

LeetCode Problem 104 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to determine the maximum depth of a binary tree. A binary tree consists of nodes where each node can have up to two children, a left child and a right child. The depth of a tree is defined as the number of nodes along the longest path from the...

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LeetCode 1367 - Linked List in Binary Tree

LeetCode Problem 1367 Difficulty: 🟡 Medium Topics: Linked List, Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks whether a linked list appears as a continuous downward path inside a binary tree. The path does not need to start at the root of the tree, but once it starts, it must move only downward through child pointers, either left or right at each step. The linked list is...

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LeetCode 965 - Univalued Binary Tree

LeetCode Problem 965 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution LeetCode 965 - Univalued Binary Tree Problem Understanding The problem gives us the root node of a binary tree and asks whether the tree is "uni-valued". A binary tree is considered uni-valued if every node in the tree contains exactly the same integer value. In simpler terms, we need to examine every node in the...

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LeetCode 99 - Recover Binary Search Tree

LeetCode Problem 99 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding The problem gives us the root of a binary search tree, but exactly two nodes in the tree have had their values swapped accidentally. Our task is to restore the tree so that it once again satisfies the binary search tree property, without modifying the tree structure itself. A binary search tree,...

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LeetCode 333 - Largest BST Subtree

LeetCode Problem 333 Difficulty: 🟡 Medium Topics: Dynamic Programming, Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding The problem gives us the root of an arbitrary binary tree and asks us to find the size of the largest subtree that is also a valid Binary Search Tree, abbreviated as BST. A subtree is any node together with all of its descendants. This means we cannot selectively ignore...

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LeetCode 108 - Convert Sorted Array to Binary Search Tree

LeetCode Problem 108 Difficulty: 🟢 Easy Topics: Array, Divide and Conquer, Tree, Binary Search Tree, Binary Tree Solution Problem Understanding The problem gives us a sorted integer array nums in strictly increasing order and asks us to convert it into a height-balanced binary search tree (BST) . A binary search tree is a binary tree where: Every node in the left subtree contains values smaller than the current node. Every...

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LeetCode 173 - Binary Search Tree Iterator

LeetCode Problem 173 Difficulty: 🟡 Medium Topics: Stack, Tree, Design, Binary Search Tree, Binary Tree, Iterator Solution It looks like your prompt accidentally concatenated two problems. I will answer the second one, LeetCode 173 - Binary Search Tree Iterator , following your required format. Problem Understanding This problem asks us to design an iterator for a Binary Search Tree (BST) that returns values in in-order traversal order . In a...

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LeetCode 129 - Sum Root to Leaf Numbers

LeetCode Problem 129 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem gives us the root of a binary tree where every node contains a single digit from 0 to 9 . Every path starting from the root and ending at a leaf node forms a number by concatenating the digits along that path. For example, consider the path: 1 -> 2 -> 3 This...

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LeetCode 1609 - Even Odd Tree

LeetCode Problem 1609 Difficulty: 🟡 Medium Topics: Tree, Breadth-First Search, Binary Tree Solution Here’s a fully detailed, reference-style solution guide for LeetCode 1609 - Even Odd Tree , following all your formatting rules: Problem Understanding The problem asks us to determine whether a given binary tree satisfies the Even-Odd Tree property. In other words, we need to validate two main conditions based on the level of the tree: For even-indexed...

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LeetCode 1448 - Count Good Nodes in Binary Tree

LeetCode Problem 1448 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem gives us the root of a binary tree and asks us to count how many nodes are considered "good". A node is called good if, along the path from the root to that node, there is no node with a value greater than the current node's value. In other words, the...

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LeetCode 1022 - Sum of Root To Leaf Binary Numbers

LeetCode Problem 1022 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem gives us the root of a binary tree where every node contains either 0 or 1 . Each path from the root node to a leaf node represents a binary number, where the root contributes the most significant bit and each child adds another bit to the right. For example, consider a path:...

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LeetCode 513 - Find Bottom Left Tree Value

LeetCode Problem 513 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to find the leftmost value in the last row of a binary tree. A binary tree is a hierarchical data structure where each node has at most two children: a left child and a right child. The input to the problem is the root node of the tree, which...

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LeetCode 1305 - All Elements in Two Binary Search Trees

LeetCode Problem 1305 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Search Tree, Sorting, Binary Tree Solution Problem Understanding The problem gives us two binary search trees, root1 and root2 . A binary search tree, commonly abbreviated as BST, has the important property that for every node: All values in the left subtree are smaller than the node's value All values in the right subtree are larger than the node's...

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LeetCode 110 - Balanced Binary Tree

LeetCode Problem 110 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to determine whether a given binary tree is height-balanced . A binary tree is considered height-balanced if, for every node in the tree, the height difference between its left and right subtrees is at most 1 . In simpler terms, the tree should not be heavily skewed to one side at...

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LeetCode 285 - Inorder Successor in BST

LeetCode Problem 285 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding This problem asks us to find the in-order successor of a given node p inside a Binary Search Tree, abbreviated as BST. An in-order traversal of a BST visits nodes in sorted order: Traverse the left subtree Visit the current node Traverse the right subtree Because BSTs maintain the ordering property: Every...

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LeetCode 1372 - Longest ZigZag Path in a Binary Tree

LeetCode Problem 1372 Difficulty: 🟡 Medium Topics: Dynamic Programming, Tree, Depth-First Search, Binary Tree Solution Problem Understanding In this problem, we are given the root node of a binary tree, and we need to find the length of the longest ZigZag path that exists anywhere inside the tree. A ZigZag path alternates directions at every step. If we move left from one node, then the next move must go right....

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LeetCode 222 - Count Complete Tree Nodes

LeetCode Problem 222 Difficulty: 🟢 Easy Topics: Binary Search, Bit Manipulation, Tree, Binary Tree Solution Problem Understanding The problem asks us to count how many nodes exist in a complete binary tree. A complete binary tree has a very specific structure. Every level except possibly the last one is completely filled, and the nodes on the final level appear as far left as possible. The input is the root node...

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LeetCode 1261 - Find Elements in a Contaminated Binary Tree

LeetCode Problem 1261 Difficulty: 🟡 Medium Topics: Hash Table, Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree Solution Problem Understanding The problem gives us a binary tree where every node value has been contaminated and replaced with -1 . However, we know the exact rule that originally generated the values in the tree. The original tree followed these rules: The root node always had value 0 If a node had...

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LeetCode 270 - Closest Binary Search Tree Value

LeetCode Problem 270 Difficulty: 🟢 Easy Topics: Binary Search, Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding The problem gives us the root of a Binary Search Tree, abbreviated as BST, and a floating point target value. Our task is to return the integer value stored in the BST that is numerically closest to the target. A Binary Search Tree has a very important property: Every node...

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LeetCode 113 - Path Sum II

LeetCode Problem 113 Difficulty: 🟡 Medium Topics: Backtracking, Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to find all root-to-leaf paths in a binary tree where the sum of the node values equals a given targetSum . A binary tree is provided through the root node, and every node contains an integer value. We are also given an integer targetSum . Our task is to explore...

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LeetCode 1597 - Build Binary Expression Tree From Infix Expression

LeetCode Problem 1597 Difficulty: 🔴 Hard Topics: String, Stack, Tree, Binary Tree Solution Problem Understanding The problem asks us to construct a binary expression tree from a valid infix arithmetic expression string. An infix expression is the standard mathematical notation where operators appear between operands, such as 3+4 or 2*(5-1) . The input string may contain: Single digit operands Operators: + , - , * , / Parentheses ( and...

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LeetCode 298 - Binary Tree Longest Consecutive Sequence

LeetCode Problem 298 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to find the length of the longest consecutive sequence path in a binary tree, where a consecutive sequence path is defined as a path in which the values increase by exactly one from parent to child. The path must move downward , meaning from a node to its children, and cannot...

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LeetCode 572 - Subtree of Another Tree

LeetCode Problem 572 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, String Matching, Binary Tree, Hash Function Solution LeetCode 572 - Subtree of Another Tree Problem Understanding This problem asks us to determine whether one binary tree appears as an exact subtree inside another binary tree. We are given two binary trees: root , the main tree subRoot , the candidate subtree We must return true if there exists some node...

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LeetCode 156 - Binary Tree Upside Down

LeetCode Problem 156 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to transform a binary tree into its "upside-down" version. In more precise terms, we are given a binary tree where every right node either has a left sibling or is absent, and no right node has children. The transformation involves rotating the tree so that the leftmost path becomes the new...

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LeetCode 545 - Boundary of Binary Tree

LeetCode Problem 545 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to compute the boundary traversal of a binary tree in a very specific order. The boundary is formed by combining four parts: The root node The left boundary, excluding leaves All leaf nodes from left to right The right boundary in reverse order, excluding leaves The challenge is not simply traversing...

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LeetCode 623 - Add One Row to Tree

LeetCode Problem 623 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to modify a binary tree by adding a new row of nodes with a given value val at a specified depth depth . The input consists of the root of a binary tree, the integer value val to insert, and the target depth depth . Depth is defined such...

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LeetCode 501 - Find Mode in Binary Search Tree

LeetCode Problem 501 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding This problem asks us to find the mode(s) in a Binary Search Tree (BST). A mode is the value that appears most frequently in the tree. Since duplicates are allowed in this BST definition, a value may occur multiple times. The input is the root node of a BST. Every node contains...

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LeetCode 654 - Maximum Binary Tree

LeetCode Problem 654 Difficulty: 🟡 Medium Topics: Array, Divide and Conquer, Stack, Tree, Monotonic Stack, Binary Tree Solution Problem Understanding The problem asks us to construct a maximum binary tree from a given integer array nums with unique elements. A maximum binary tree is a binary tree where each node is the maximum element of the subarray it represents. Specifically, the root of the tree is the largest element in...

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LeetCode 543 - Diameter of Binary Tree

LeetCode Problem 543 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to compute the diameter of a binary tree. The diameter is defined as the length of the longest path between any two nodes , measured in number of edges. Importantly, this path does not need to pass through the root of the tree. In other words, the path can lie entirely...

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LeetCode 1628 - Design an Expression Tree With Evaluate Function

LeetCode Problem 1628 Difficulty: 🟡 Medium Topics: Array, Math, Stack, Tree, Design, Binary Tree Solution Problem Understanding The problem requires constructing a binary expression tree from a postfix arithmetic expression and implementing a method to evaluate the tree. The input is an array of strings postfix representing numbers and operators ( + , - , * , / ) in postfix notation , meaning operands appear before their operators. The...

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LeetCode 662 - Maximum Width of Binary Tree

LeetCode Problem 662 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to compute the maximum width among all levels of a binary tree. The important detail is that the width is not simply the number of non-null nodes at a level. Instead, the width must include the positions of missing nodes that would exist if the tree were represented as...

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LeetCode 297 - Serialize and Deserialize Binary Tree

LeetCode Problem 297 Difficulty: 🔴 Hard Topics: String, Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree Solution Problem Understanding The problem asks us to design two complementary operations for a binary tree: serialization and deserialization. Serialization converts a binary tree into a string representation that can be stored or transmitted. Deserialization performs the reverse operation, reconstructing the exact same binary tree structure from the serialized string. The important detail is...

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LeetCode 95 - Unique Binary Search Trees II

LeetCode Problem 95 Difficulty: 🟡 Medium Topics: Dynamic Programming, Backtracking, Tree, Binary Search Tree, Binary Tree Solution Problem Understanding The problem asks us to generate all structurally unique binary search trees (BSTs) that contain exactly n nodes labeled from 1 to n . A BST is a binary tree where for every node, all values in the left subtree are smaller than the node, and all values in the right...

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LeetCode 863 - All Nodes Distance K in Binary Tree

LeetCode Problem 863 Difficulty: 🟡 Medium Topics: Hash Table, Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution LeetCode 863 - All Nodes Distance K in Binary Tree Problem Understanding This problem gives us the root of a binary tree, a specific target node inside that tree, and an integer k . Our task is to return all node values whose distance from the target node is exactly k . The...

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LeetCode 1650 - Lowest Common Ancestor of a Binary Tree III

LeetCode Problem 1650 Difficulty: 🟡 Medium Topics: Hash Table, Two Pointers, Tree, Binary Tree Solution Problem Understanding This problem asks us to find the lowest common ancestor, usually abbreviated as LCA, of two nodes in a binary tree. Unlike the classic version of the problem, every node contains a direct pointer to its parent. That extra parent reference changes the way we can solve the problem efficiently. The input gives...

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LeetCode 1008 - Construct Binary Search Tree from Preorder Traversal

LeetCode Problem 1008 Difficulty: 🟡 Medium Topics: Array, Stack, Tree, Binary Search Tree, Monotonic Stack, Binary Tree Solution Let's dive deep and construct a thorough technical guide for LeetCode 1008, following your formatting rules. Problem Understanding The problem asks us to construct a binary search tree (BST) from a given preorder traversal array. A preorder traversal is defined as visiting the root node first, then recursively visiting the left subtree,...

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LeetCode 1339 - Maximum Product of Splitted Binary Tree

LeetCode Problem 1339 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution That is a long, structured technical document with multiple required sections, complete Python and Go implementations, worked examples, test tables, and edge case analysis. To ensure I follow your formatting rules exactly and keep the guide readable, I should provide it as a canvas document. I’ll generate the full detailed solution guide for LeetCode 1339 - Maximum...

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LeetCode 337 - House Robber III

LeetCode Problem 337 Difficulty: 🟡 Medium Topics: Dynamic Programming, Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem is a variation of the classic House Robber dynamic programming problem, but instead of houses being arranged in a straight line, the houses form a binary tree. Each node in the binary tree represents a house, and the value stored in the node represents the amount of money available in that...

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LeetCode 1676 - Lowest Common Ancestor of a Binary Tree IV

LeetCode Problem 1676 Difficulty: 🟡 Medium Topics: Hash Table, Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to find the Lowest Common Ancestor, or LCA, of multiple nodes in a binary tree. Unlike the classic LCA problem that involves only two nodes, this variation generalizes the definition to any number of target nodes. The input consists of: root , the root node of a binary tree...

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LeetCode 515 - Find Largest Value in Each Tree Row

LeetCode Problem 515 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to find the largest value in each row of a binary tree, where a row is defined as all nodes at the same depth. The input is the root of a binary tree, which may contain up to 10,000 nodes, and each node's value is a signed 32-bit integer....

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LeetCode 111 - Minimum Depth of Binary Tree

LeetCode Problem 111 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to determine the minimum depth of a binary tree. In other words, given the root of a binary tree, we want to find the shortest path from the root node down to the nearest leaf node. A leaf node is explicitly defined as a node with no children, meaning...

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LeetCode 103 - Binary Tree Zigzag Level Order Traversal

LeetCode Problem 103 Difficulty: 🟡 Medium Topics: Tree, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to perform a level order traversal of a binary tree, but with a twist. Instead of always traversing each level from left to right, we alternate the traversal direction at every level. A normal level order traversal, also called Breadth-First Search (BFS), visits nodes level by level starting from the root....

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LeetCode 1161 - Maximum Level Sum of a Binary Tree

LeetCode Problem 1161 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding In this problem, we are given the root node of a binary tree. Every node belongs to a specific level in the tree. The root is at level 1 , its direct children are at level 2 , their children are at level 3 , and so on. Our goal is to compute...

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LeetCode 510 - Inorder Successor in BST II

LeetCode Problem 510 Difficulty: 🟡 Medium Topics: Tree, Binary Search Tree, Binary Tree Solution Problem Understanding This problem asks us to find the in-order successor of a given node inside a Binary Search Tree, abbreviated as BST. Unlike the classic version of the problem, we are not given access to the root of the tree. Instead, we are given only a pointer to a specific node, and each node contains...

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LeetCode 865 - Smallest Subtree with all the Deepest Nodes

LeetCode Problem 865 Difficulty: 🟡 Medium Topics: Hash Table, Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem gives us the root of a binary tree and asks us to find the smallest subtree that contains all of the deepest nodes in the tree. The depth of a node is defined as the number of edges between that node and the root. The root itself has depth...

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LeetCode 1382 - Balance a Binary Search Tree

LeetCode Problem 1382 Difficulty: 🟡 Medium Topics: Divide and Conquer, Greedy, Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Here is a complete, detailed technical solution guide for LeetCode 1382 - Balance a Binary Search Tree , following all your formatting rules. Problem Understanding The problem asks us to take a binary search tree (BST) that may be unbalanced and produce a new BST that is balanced while preserving...

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LeetCode 1123 - Lowest Common Ancestor of Deepest Leaves

LeetCode Problem 1123 Difficulty: 🟡 Medium Topics: Hash Table, Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding This problem asks us to find the lowest common ancestor, abbreviated as LCA, of all the deepest leaf nodes in a binary tree. A leaf node is any node with no children. The depth of the root is 0 , and every level downward increases the depth by 1 . The...

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LeetCode 1120 - Maximum Average Subtree

LeetCode Problem 1120 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to find the maximum average value among all subtrees of a given binary tree. A subtree is defined as any node along with all of its descendants. The average of a subtree is the sum of its node values divided by the number of nodes in that subtree. The input is...

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LeetCode 1457 - Pseudo-Palindromic Paths in a Binary Tree

LeetCode Problem 1457 Difficulty: 🟡 Medium Topics: Bit Manipulation, Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding This problem asks us to count how many root to leaf paths in a binary tree are "pseudo-palindromic". A palindrome is a sequence that reads the same forward and backward. For example, [1,2,1] and [3,4,4,3] are palindromes. The important property of a palindrome is that at most one value may appear...

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LeetCode 1038 - Binary Search Tree to Greater Sum Tree

LeetCode Problem 1038 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding The problem gives us the root of a Binary Search Tree, abbreviated as BST, and asks us to transform it into a Greater Sum Tree. In a Binary Search Tree, every node follows an important ordering rule: All values in the left subtree are smaller than the current node. All values in...

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LeetCode 701 - Insert into a Binary Search Tree

LeetCode Problem 701 Difficulty: 🟡 Medium Topics: Tree, Binary Search Tree, Binary Tree Solution Problem Understanding This problem asks us to insert a new value into an existing Binary Search Tree, abbreviated as BST, while preserving the BST property. A Binary Search Tree is a binary tree with a special ordering rule: Every value in the left subtree of a node is smaller than the node’s value. Every value in...

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LeetCode 1080 - Insufficient Nodes in Root to Leaf Paths

LeetCode Problem 1080 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to prune a binary tree by removing insufficient nodes . A node is insufficient if every root-to-leaf path passing through it has a sum strictly less than the given limit . The input is the root of a binary tree and an integer limit . The output should be the root...

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LeetCode 1430 - Check If a String Is a Valid Sequence from Root to Leaves Path in a Binary Tree

LeetCode Problem 1430 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to determine whether a given array of integers arr represents a valid sequence from the root to a leaf in a binary tree. Each node in the tree has a value between 0 and 9, and a valid sequence is defined as a path starting from the root node...

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LeetCode 663 - Equal Tree Partition

LeetCode Problem 663 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks whether it is possible to split a binary tree into two separate trees such that both resulting trees have the same sum of node values. The split must happen by removing exactly one edge from the original tree. A binary tree is given through its root node. Every node contains an integer...

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LeetCode 742 - Closest Leaf in a Binary Tree

LeetCode Problem 742 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to find the closest leaf node to a given target node k in a binary tree. The input is the root of a binary tree where each node has a unique integer value . A leaf node is defined as any node without children. The output is the value...

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LeetCode 669 - Trim a Binary Search Tree

LeetCode Problem 669 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding LeetCode 669, Trim a Binary Search Tree, asks us to modify a binary search tree so that every remaining node has a value within the inclusive range [low, high] . The input consists of three parts: root , the root node of a valid binary search tree low , the minimum allowed...

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LeetCode 687 - Longest Univalue Path

LeetCode Problem 687 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to find the longest path in a binary tree where every node along the path has the same value . The key detail is that the path length is measured in edges , not nodes. Additionally, the path does not need to pass through the root , meaning the longest valid...

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LeetCode 1569 - Number of Ways to Reorder Array to Get Same BST

LeetCode Problem 1569 Difficulty: 🔴 Hard Topics: Array, Math, Divide and Conquer, Dynamic Programming, Tree, Union-Find, Binary Search Tree, Memoization, Combinatorics, Binary Tree Solution Problem Understanding The problem gives us a permutation of integers from 1 to n , and we insert the numbers into an initially empty Binary Search Tree (BST) in the exact order they appear in the array. A BST has the following property: Values smaller than...

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LeetCode 1325 - Delete Leaves With a Given Value

LeetCode Problem 1325 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to repeatedly remove leaf nodes from a binary tree if their value matches a given target . A leaf node is a node with no children, meaning both its left and right pointers are null (or None in Python). At first glance, the task may appear simple: traverse the tree and...

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LeetCode 1660 - Correct a Binary Tree

LeetCode Problem 1660 Difficulty: 🟡 Medium Topics: Hash Table, Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Here is a complete, detailed technical solution guide for LeetCode 1660 - Correct a Binary Tree , formatted exactly as requested. Problem Understanding The problem presents a binary tree that has a subtle defect: there is exactly one invalid node , whose right child incorrectly points to another node on the same depth...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 979 - Distribute Coins in Binary Tree

LeetCode Problem 979 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding In this problem, we are given a binary tree where every node contains some number of coins. The total number of coins across the entire tree is exactly equal to the number of nodes in the tree. Our goal is to redistribute the coins so that every node ends up with exactly one coin. A...

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LeetCode 1361 - Validate Binary Tree Nodes

LeetCode Problem 1361 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Breadth-First Search, Union-Find, Graph Theory, Binary Tree Solution Problem Understanding The problem gives us n nodes labeled from 0 to n - 1 . For every node i , we are told which node is its left child and which node is its right child through the arrays leftChild and rightChild . If leftChild[i] = x , then node x...

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LeetCode 2005 - Subtree Removal Game with Fibonacci Tree

LeetCode Problem 2005 Difficulty: 🔴 Hard Topics: Math, Dynamic Programming, Tree, Binary Tree, Game Theory Solution LeetCode 2005 - Subtree Removal Game with Fibonacci Tree Problem Understanding The problem defines a special kind of binary tree called a Fibonacci tree. The structure is recursive: order(0) is an empty tree. order(1) is a single node. order(n) has: a root node, a left subtree equal to order(n - 2) , a right...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 114 - Flatten Binary Tree to Linked List

LeetCode Problem 114 Difficulty: 🟡 Medium Topics: Linked List, Stack, Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to transform a binary tree into a flattened structure that behaves like a singly linked list. The transformation must happen in-place, meaning we are not supposed to create an entirely new tree or list structure. Instead, we must rearrange the existing pointers inside the tree nodes. The flattened...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 235 - Lowest Common Ancestor of a Binary Search Tree

LeetCode Problem 235 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding The problem asks us to find the Lowest Common Ancestor, commonly abbreviated as LCA, of two nodes in a Binary Search Tree (BST). A lowest common ancestor of two nodes p and q is the deepest node in the tree that has both p and q as descendants. A node is allowed...

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LeetCode 653 - Two Sum IV - Input is a BST

LeetCode Problem 653 Difficulty: 🟢 Easy Topics: Hash Table, Two Pointers, Tree, Depth-First Search, Breadth-First Search, Binary Search Tree, Binary Tree Solution LeetCode 653, Two Sum IV - Input is a BST Problem Understanding This problem gives us the root of a Binary Search Tree (BST) and an integer k . We must determine whether there are two distinct nodes in the tree whose values add up to k ....

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1666 - Change the Root of a Binary Tree

LeetCode Problem 1666 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to reroot a binary tree at a given leaf node. Normally, a binary tree has a single root, and every node points downward to its children. In this problem, each node also contains a parent pointer, which allows traversal upward toward the root. We are given two inputs: root , the...

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LeetCode 1373 - Maximum Sum BST in Binary Tree

LeetCode Problem 1373 Difficulty: 🔴 Hard Topics: Dynamic Programming, Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding This problem asks us to examine every possible subtree inside a binary tree and determine whether that subtree forms a valid Binary Search Tree, abbreviated as BST. Among all valid BST subtrees, we must return the maximum possible sum of node values. A subtree consists of a node together with...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 437 - Path Sum III

LeetCode Problem 437 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem gives us the root of a binary tree and an integer targetSum . We need to count how many downward paths in the tree have values that add up exactly to targetSum . A path can begin at any node and end at any node, as long as it always moves downward from...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1602 - Find Nearest Right Node in Binary Tree

LeetCode Problem 1602 Difficulty: 🟡 Medium Topics: Tree, Breadth-First Search, Binary Tree Solution Problem Understanding This problem asks us to find the nearest node to the right of a given node u on the same level of a binary tree. A binary tree is organized into levels. The root is on level 0 , its children are on level 1 , their children are on level 2 , and so...

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LeetCode 814 - Binary Tree Pruning

LeetCode Problem 814 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution LeetCode 814 - Binary Tree Pruning Problem Understanding This problem asks us to modify a binary tree by removing every subtree that does not contain at least one node with value 1 . A subtree consists of a node and all of its descendants. If an entire subtree contains only 0 values, then that subtree should be...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 951 - Flip Equivalent Binary Trees

LeetCode Problem 951 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution LeetCode 951 - Flip Equivalent Binary Trees Problem Understanding This problem asks us to determine whether two binary trees can be made identical by performing a special operation called a flip. A flip operation can be applied at any node, and it simply swaps that node’s left and right child subtrees. The important detail is that we...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1145 - Binary Tree Coloring Game

LeetCode Problem 1145 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem is a two-player game played on a binary tree, where each player colors nodes starting from an initial chosen node. Player 1 picks a node x and colors it red, while Player 2 picks a different node y and colors it blue. Players then alternate turns, coloring an uncolored neighbor (parent, left child,...

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LeetCode 1104 - Path In Zigzag Labelled Binary Tree

LeetCode Problem 1104 Difficulty: 🟡 Medium Topics: Math, Tree, Binary Tree Solution Problem Understanding This problem describes an infinite binary tree where nodes are normally arranged level by level, but with a twist in how labels are assigned. In a standard binary tree, nodes in each level are labeled from left to right. Here, the labeling alternates direction depending on the row number. Odd numbered rows, such as row 1,...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 109 - Convert Sorted List to Binary Search Tree

LeetCode Problem 109 Difficulty: 🟡 Medium Topics: Linked List, Divide and Conquer, Tree, Binary Search Tree, Binary Tree Solution Problem Understanding The problem gives us the head of a singly linked list whose values are already sorted in ascending order. We must convert this linked list into a height balanced Binary Search Tree, usually abbreviated as BST. A Binary Search Tree has the property that: Every node in the left...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 257 - Binary Tree Paths

LeetCode Problem 257 Difficulty: 🟢 Easy Topics: String, Backtracking, Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to return every path from the root of a binary tree to each leaf node. A root-to-leaf path is formed by starting at the root node and continuously moving downward through child nodes until reaching a node that has no children. The input is the root node of a...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 998 - Maximum Binary Tree II

LeetCode Problem 998 Difficulty: 🟡 Medium Topics: Tree, Binary Tree Solution LeetCode 998 - Maximum Binary Tree II Problem Statement A maximum tree is a special binary tree where every node contains a value greater than all values inside its subtree. The tree is built recursively from an array by choosing the maximum element as the root, then recursively constructing the left subtree from the elements before the maximum value...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 703 - Kth Largest Element in a Stream

LeetCode Problem 703 Difficulty: 🟢 Easy Topics: Tree, Design, Binary Search Tree, Heap (Priority Queue), Binary Tree, Data Stream Solution Problem Understanding The problem asks us to design a data structure that continuously tracks the kth largest element in a stream of integers. We are given an integer k and an initial list of numbers called nums . After initialization, new numbers are added one at a time using the...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 431 - Encode N-ary Tree to Binary Tree

LeetCode Problem 431 Difficulty: 🔴 Hard Topics: Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree Solution Problem Understanding This problem asks us to design a reversible transformation between two different tree structures: An N-ary tree, where each node can have any number of children A binary tree, where each node has at most two children The important requirement is not how the encoding looks internally, but that the process is...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 776 - Split BST

LeetCode Problem 776 Difficulty: 🟡 Medium Topics: Tree, Binary Search Tree, Recursion, Binary Tree Solution Problem Understanding The problem asks us to split a binary search tree (BST) into two separate subtrees based on a target value. Specifically, the first subtree should contain all nodes with values less than or equal to the target, and the second subtree should contain all nodes with values strictly greater than the target. Importantly,...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 272 - Closest Binary Search Tree Value II

LeetCode Problem 272 Difficulty: 🔴 Hard Topics: Two Pointers, Stack, Tree, Depth-First Search, Binary Search Tree, Heap (Priority Queue), Binary Tree Solution Problem Understanding This problem asks us to find the k values in a Binary Search Tree, or BST, whose values are numerically closest to a given floating point target . A BST has a very important property: Every value in the left subtree is smaller than the current...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 508 - Most Frequent Subtree Sum

LeetCode Problem 508 Difficulty: 🟡 Medium Topics: Hash Table, Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to compute the subtree sum for every node in a binary tree, then determine which subtree sum appears most frequently. A subtree rooted at a node includes that node and all of its descendants. The subtree sum is simply the sum of every value contained in that subtree. For...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 968 - Binary Tree Cameras

LeetCode Problem 968 Difficulty: 🔴 Hard Topics: Dynamic Programming, Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to determine the minimum number of cameras required to monitor all nodes in a binary tree. Each camera placed on a node can monitor its parent, itself, and its immediate children. The input is the root of a binary tree, where each node has a value 0 and may...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 987 - Vertical Order Traversal of a Binary Tree

LeetCode Problem 987 Difficulty: 🔴 Hard Topics: Hash Table, Tree, Depth-First Search, Breadth-First Search, Sorting, Binary Tree Solution Problem Understanding The problem asks us to compute the vertical order traversal of a binary tree. In simpler terms, we are asked to “look at the tree from the side” and collect the nodes that align in the same vertical column. Each node has a position defined by (row, col) where row...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 538 - Convert BST to Greater Tree

LeetCode Problem 538 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding This problem asks us to transform a Binary Search Tree, abbreviated as BST, into a "Greater Tree". In the transformed tree, every node's value should become: its original value plus the sum of all values greater than it in the original BST The structure of the tree does not change. Only the...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 116 - Populating Next Right Pointers in Each Node

LeetCode Problem 116 Difficulty: 🟡 Medium Topics: Linked List, Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding This problem asks us to populate the next pointers of nodes in a perfect binary tree . A perfect binary tree has all levels completely filled; every internal node has exactly two children, and all leaves are at the same depth. The next pointer of a node should point to the...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1644 - Lowest Common Ancestor of a Binary Tree II

LeetCode Problem 1644 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to find the lowest common ancestor (LCA) of two given nodes, p and q , in a binary tree, under the condition that either node might not exist in the tree . In other words, given a binary tree with unique values and two target nodes, we must determine the deepest...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 530 - Minimum Absolute Difference in BST

LeetCode Problem 530 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding This problem gives us the root node of a Binary Search Tree, abbreviated as BST, and asks us to find the minimum absolute difference between the values of any two distinct nodes in the tree. A Binary Search Tree has a very important property: Every value in the left subtree...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 919 - Complete Binary Tree Inserter

LeetCode Problem 919 Difficulty: 🟡 Medium Topics: Tree, Breadth-First Search, Design, Binary Tree Solution Problem Understanding This problem asks us to design a data structure that allows insertion into a complete binary tree while maintaining its completeness. A complete binary tree is one where all levels are fully filled, except possibly the last, which is filled from left to right. The key requirement is that after each insertion, the tree...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 889 - Construct Binary Tree from Preorder and Postorder Traversal

LeetCode Problem 889 Difficulty: 🟡 Medium Topics: Array, Hash Table, Divide and Conquer, Tree, Binary Tree Solution Problem Understanding The problem gives us two traversal orders of the same binary tree: preorder , which visits nodes in the order: root → left subtree → right subtree postorder , which visits nodes in the order: left subtree → right subtree → root Our task is to reconstruct and return the binary...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 102 - Binary Tree Level Order Traversal

LeetCode Problem 102 Difficulty: 🟡 Medium Topics: Tree, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to perform a level order traversal on a binary tree. A binary tree is a hierarchical structure where each node can have at most two children, commonly referred to as the left child and the right child. A level order traversal means we visit the tree one level at a time,...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 236 - Lowest Common Ancestor of a Binary Tree

LeetCode Problem 236 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to find the Lowest Common Ancestor, usually abbreviated as LCA, of two nodes in a binary tree. A binary tree consists of nodes where each node may have a left child and a right child. We are given three inputs: root , which is the root node of the binary tree...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1214 - Two Sum BSTs

LeetCode Problem 1214 Difficulty: 🟡 Medium Topics: Two Pointers, Binary Search, Stack, Tree, Depth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding The problem gives us two binary search trees, root1 and root2 , along with an integer target . We must determine whether there exists one node from the first tree and one node from the second tree such that their values add up exactly to target ....

Practice › LeetCode › LeetCode 05xx ›

LeetCode 549 - Binary Tree Longest Consecutive Sequence II

LeetCode Problem 549 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to find the length of the longest consecutive sequence path in a binary tree. Unlike the simpler version of the problem where the sequence must move strictly downward from parent to child, this version allows the path to move in a child-parent-child direction as well. A consecutive path means that adjacent...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 449 - Serialize and Deserialize BST

LeetCode Problem 449 Difficulty: 🟡 Medium Topics: String, Tree, Depth-First Search, Breadth-First Search, Design, Binary Search Tree, Binary Tree Solution Problem Understanding The problem asks us to design two operations for a Binary Search Tree, abbreviated as BST: serialize(root) converts the BST into a string representation. deserialize(data) reconstructs the exact same BST from that string. The important requirement is that the deserialized tree must match the original tree structure and...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 993 - Cousins in Binary Tree

LeetCode Problem 993 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem asks us to determine whether two nodes in a binary tree are cousins. Two nodes are considered cousins if they satisfy two conditions simultaneously: They are located at the same depth in the tree. They have different parents. The input consists of: root , which is the root node of a...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 637 - Average of Levels in Binary Tree

LeetCode Problem 637 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding In this problem, we are given the root node of a binary tree, and we need to compute the average value of all nodes at each depth level of the tree. A binary tree is organized into levels. The root node is at level 0 , its children are at level 1 ,...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 894 - All Possible Full Binary Trees

LeetCode Problem 894 Difficulty: 🟡 Medium Topics: Dynamic Programming, Tree, Recursion, Memoization, Binary Tree Solution Problem Understanding The problem asks us to generate every possible full binary tree that contains exactly n nodes. A full binary tree is a special kind of binary tree where every node has either exactly two children or no children at all. In other words, a node can never have only one child. The input...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 94 - Binary Tree Inorder Traversal

LeetCode Problem 94 Difficulty: 🟢 Easy Topics: Stack, Tree, Depth-First Search, Binary Tree Solution Binary Tree Inorder Traversal Problem Understanding This problem asks us to perform an inorder traversal on a binary tree and return the values of the visited nodes in the correct order. A binary tree is a hierarchical data structure where each node can have at most two children, a left child and a right child. The...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 988 - Smallest String Starting From Leaf

LeetCode Problem 988 Difficulty: 🟡 Medium Topics: String, Backtracking, Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem gives us the root of a binary tree where every node stores an integer between 0 and 25 . Each integer corresponds to a lowercase English letter: 0 -> 'a' 1 -> 'b' ... 25 -> 'z' We need to construct strings that begin at a leaf node and move upward...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 112 - Path Sum

LeetCode Problem 112 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding This problem asks us to determine whether a binary tree contains at least one valid root-to-leaf path whose node values add up to a given target sum. A binary tree consists of nodes where each node can have a left child and a right child. Each node also stores an integer value. The...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 106 - Construct Binary Tree from Inorder and Postorder Traversal

LeetCode Problem 106 Difficulty: 🟡 Medium Topics: Array, Hash Table, Divide and Conquer, Tree, Binary Tree Solution Problem Understanding The problem provides two traversal orders of the same binary tree: inorder , which follows the order: left subtree, root, right subtree postorder , which follows the order: left subtree, right subtree, root We must reconstruct the original binary tree and return its root node. The key challenge is understanding how...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 872 - Leaf-Similar Trees

LeetCode Problem 872 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding This problem asks us to compare two binary trees based only on their leaf nodes. A leaf node is a node that has no left child and no right child. For each tree, we must collect the leaf values in left to right order, then determine whether the two resulting sequences are identical. The important...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 700 - Search in a Binary Search Tree

LeetCode Problem 700 Difficulty: 🟢 Easy Topics: Tree, Binary Search Tree, Binary Tree Solution Problem Understanding This problem gives us the root node of a Binary Search Tree, commonly abbreviated as a BST, along with an integer value val . Our goal is to locate the node whose value is exactly equal to val and return that node. Since the problem asks us to return the subtree rooted at that...

Practice › LeetCode › LeetCode 00xx ›

LeetCode 96 - Unique Binary Search Trees

LeetCode Problem 96 Difficulty: 🟡 Medium Topics: Math, Dynamic Programming, Tree, Binary Search Tree, Binary Tree Solution LeetCode 96 - Unique Binary Search Trees Problem Understanding This problem asks us to determine how many structurally different Binary Search Trees, or BSTs, can be formed using the integers from 1 to n . A Binary Search Tree has an important property: Every value in the left subtree is smaller than the...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1586 - Binary Search Tree Iterator II

LeetCode Problem 1586 Difficulty: 🟡 Medium Topics: Stack, Tree, Design, Binary Search Tree, Binary Tree, Iterator Solution Problem Understanding The problem requires implementing a BSTIterator class that allows forward and backward traversal over the in-order sequence of a Binary Search Tree (BST). In-order traversal of a BST visits nodes in ascending order. The iterator must support four operations: next() , prev() , hasNext() , and hasPrev() . Initially, the iterator...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 783 - Minimum Distance Between BST Nodes

LeetCode Problem 783 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Search Tree, Binary Tree Solution Problem Understanding The problem asks us to find the minimum difference between values of any two nodes in a Binary Search Tree (BST). In other words, given a BST, we need to calculate the smallest absolute difference |a - b| where a and b are values of two distinct nodes. The input...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 255 - Verify Preorder Sequence in Binary Search Tree

LeetCode Problem 255 Difficulty: 🟡 Medium Topics: Array, Stack, Tree, Binary Search Tree, Recursion, Monotonic Stack, Binary Tree Solution Problem Understanding The problem gives an array of unique integers called preorder . This array is supposed to represent the preorder traversal of a binary search tree, and we must determine whether such a BST could actually exist. In a preorder traversal, nodes are visited in this order: Visit the current...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 563 - Binary Tree Tilt

LeetCode Problem 563 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem asks us to compute the total tilt of an entire binary tree. Every node in the tree has its own tilt, and the final answer is the sum of all individual node tilts. The tilt of a node is defined as the absolute difference between: The sum of all values in its left...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1379 - Find a Corresponding Node of a Binary Tree in a Clone of That Tree

LeetCode Problem 1379 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The traversal is by reference, not value.

Practice › LeetCode › LeetCode 06xx ›

LeetCode 671 - Second Minimum Node In a Binary Tree

LeetCode Problem 671 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Binary Tree Solution Problem Understanding The problem provides a special binary tree where each node either has zero or two children, and every internal node has a value equal to the smaller value among its two children. This property guarantees that the root contains the minimum value in the tree , since the root is always the smallest among its...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 226 - Invert Binary Tree

LeetCode Problem 226 Difficulty: 🟢 Easy Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem gives the root node of a binary tree and asks us to invert the tree. Inverting a binary tree means swapping the left and right child of every node in the tree. For example, if a node originally has: left child = 2 right child = 7 after inversion it becomes:...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 105 - Construct Binary Tree from Preorder and Inorder Traversal

LeetCode Problem 105 Difficulty: 🟡 Medium Topics: Array, Hash Table, Divide and Conquer, Tree, Binary Tree Solution Problem Understanding The problem is asking us to reconstruct a binary tree given two traversal orders: preorder and inorder . In a preorder traversal, nodes are visited in the order: root, left subtree, right subtree. In an inorder traversal, nodes are visited in the order: left subtree, root, right subtree. Given these two...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 199 - Binary Tree Right Side View

LeetCode Problem 199 Difficulty: 🟡 Medium Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree Solution Problem Understanding The problem gives us the root node of a binary tree and asks us to determine which nodes are visible when looking at the tree from the right side. A binary tree is a hierarchical data structure where each node can have at most two children, called the left child and the right...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1028: Recover a Tree From Preorder Traversal

Problem Restatement We run a preorder depth-first traversal on a binary tree. At each node, we output its depth (as a count of dashes) followed by its value. For example, a tree with root 1 and left child 2 and right child 5 would produce "1-2--3--4-5--6--7" for a specific tree. We are given this string traversal and need to recover the original binary tree. The official constraints state that the...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1022: Sum of Root To Leaf Binary Numbers

Problem Restatement We are given the root of a binary tree where each node has value 0 or 1 . Each root-to-leaf path represents a binary number. We need to return the sum of all these binary numbers. The official constraints state that the number of nodes is in [1, 1000] , Node.val is 0 or 1 , and the answer fits in a 32-bit integer. Input and Output Item...

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LeetCode 1080: Insufficient Nodes in Root to Leaf Paths

Problem Restatement We are given the root of a binary tree and an integer limit . A node is insufficient if every root-to-leaf path through that node has a sum strictly less than limit . We need to delete all insufficient nodes and return the root of the resulting tree. The official constraints state that the number of nodes is in [1, 5000] and -10^5 <= Node.val <= 10^5 ....

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1038: Binary Search Tree to Greater Sum Tree

Problem Restatement We are given the root of a Binary Search Tree (BST). We need to convert it into a Greater Sum Tree (GST) where every node's value is replaced by the sum of all values greater than or equal to that node's original value in the tree. The official constraints state that the number of nodes is in [1, 100] and 0 <= Node.val <= 100 . Input and...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1026: Maximum Difference Between Node and Ancestor

Problem Restatement We are given the root of a binary tree. For every pair of a node v and an ancestor u , we want to maximize: abs(v.val - u.val) We need to return the maximum such value over all valid ancestor-descendant pairs. The official constraints state that the number of nodes is in [2, 5000] and 0 <= Node.val <= 10^5 . Input and Output Item Meaning Input Root...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1008: Construct Binary Search Tree from Preorder Traversal

Problem Restatement We are given the preorder traversal of a binary search tree (BST) in an array preorder . We need to reconstruct the BST and return its root. Recall that in a BST, for every node, all values in the left subtree are smaller, and all values in the right subtree are larger. In preorder traversal, we visit the root before the left and right subtrees. The official constraints...

Practice › LeetCode › LeetCode (archived) › LeetCode 09xx ›

LeetCode 971: Flip Binary Tree To Match Preorder Traversal

Problem Restatement We are given a binary tree and an array voyage . A flip operation at a node swaps its left and right children. We need to flip the smallest number of nodes so that the preorder traversal of the tree becomes exactly equal to voyage . Preorder traversal visits nodes in this order: root left subtree right subtree If it is possible, return the values of the flipped...

Practice › LeetCode › LeetCode (archived) › LeetCode 09xx ›

LeetCode 968: Binary Tree Cameras

Problem Restatement We are given the root of a binary tree. We may install cameras on tree nodes. A camera at a node can monitor: Its parent Itself Its immediate children Return the minimum number of cameras needed to monitor every node in the tree. The official constraints say the tree has between 1 and 1000 nodes, and every node value is 0 . Input and Output Item Meaning Input...

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LeetCode 998: Maximum Binary Tree II

Problem Restatement We are given the root of a maximum binary tree and an integer val . The tree was originally built from an array a using this rule: The largest value in a becomes the root. The left subtree is built from the elements to the left of that largest value. The right subtree is built from the elements to the right of that largest value. Now we append...

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LeetCode 919: Complete Binary Tree Inserter

Problem Restatement We need to design a class called CBTInserter . It is initialized with the root of a complete binary tree. A complete binary tree has every level full except possibly the last level, and the last level is filled from left to right. The class must support: Method Meaning CBTInserter(root) Initialize with an existing complete binary tree insert(val) Insert a new node while keeping the tree complete, and...

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LeetCode 897: Increasing Order Search Tree

Problem Restatement We are given the root of a binary search tree. We need to rearrange the tree in inorder order so that: Requirement Meaning New root The leftmost node of the original tree Left child Every node must have no left child Right child Each node may have one right child Order Nodes appear in increasing order The result should be a right-skewed tree, like a sorted linked list...

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LeetCode 872: Leaf-Similar Trees

Problem Restatement We are given the roots of two binary trees: root1 root2 For each tree, collect all leaf values from left to right. A leaf node is a node with no left child and no right child. Two trees are leaf-similar if their leaf value sequences are the same. Return True if the two trees are leaf-similar. Otherwise, return False . Input and Output Item Meaning Input root1 ,...

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LeetCode 965: Univalued Binary Tree

Problem Restatement We are given the root of a binary tree. A binary tree is univalued if every node in the tree has the same value. Return true if every node has the same value. Otherwise, return false . The official constraints say the tree has between 1 and 100 nodes, and each node value is in the range [0, 99] . Input and Output Item Meaning Input root ,...

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LeetCode 894: All Possible Full Binary Trees

Problem Restatement We are given an integer n . Return a list of all possible full binary trees with exactly n nodes. A full binary tree is a binary tree where every node has either: Children count Meaning 0 Leaf node 2 Internal node No node may have exactly one child. Each node has value 0 . We only care about the tree shapes. LeetCode asks for all possible full...

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LeetCode 993: Cousins in Binary Tree

Problem Restatement We are given the root of a binary tree with unique values. We are also given two different values: x y Both values exist in the tree. We need to return True if the nodes with values x and y are cousins. Two nodes are cousins if: Condition Meaning Same depth They are on the same tree level Different parents They do not share the same immediate parent...

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LeetCode 250: Count Univalue Subtrees

Problem Restatement We are given the root of a binary tree. Return the number of uni-value subtrees. A uni-value subtree means every node in that subtree has the same value. An empty tree has 0 uni-value subtrees. The constraints say the tree has between 0 and 1000 nodes, and each node value is between -1000 and 1000 . Input and Output Item Meaning Input Root of a binary tree Output...

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LeetCode 865: Smallest Subtree with all the Deepest Nodes

Problem Restatement We are given the root of a binary tree. The depth of a node is its shortest distance from the root. A deepest node is a node with the largest depth in the whole tree. We need to return the smallest subtree that contains all deepest nodes. Since a subtree is represented by its root node, we return the root of that smallest subtree. Another way to say...

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LeetCode 623: Add One Row to Tree

Problem Restatement We are given the root of a binary tree and two integers val and depth . We need to add a new row of nodes with value val at the given depth . The root is at depth 1 . If depth == 1 , we create a new root with value val . The original tree becomes the left child of the new root. Otherwise, for every...

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LeetCode 889: Construct Binary Tree from Preorder and Postorder Traversal

Problem Restatement We are given two arrays: Array Meaning preorder Preorder traversal of a binary tree postorder Postorder traversal of the same binary tree The binary tree contains distinct values. We need to reconstruct and return one possible binary tree. If multiple valid trees exist, returning any one of them is accepted. The problem guarantees that both traversals come from the same binary tree. Preorder traversal visits nodes in this...

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LeetCode 988: Smallest String Starting From Leaf

Problem Restatement We are given the root of a binary tree. Each node has a value from 0 to 25 . Each value maps to a lowercase English letter: Value Letter 0 "a" 1 "b" 2 "c" ... ... 25 "z" We need to return the lexicographically smallest string that starts at a leaf and ends at the root. A leaf is a node with no children. The number of...

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LeetCode 814: Binary Tree Pruning

Problem Restatement We are given the root of a binary tree. Every node has value either 0 or 1 . We need to remove every subtree that does not contain a 1 . A subtree means a node together with all of its descendants. If a subtree has only 0 values, that entire subtree should be removed. Return the root of the pruned tree. The official problem asks us to...

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LeetCode 987: Vertical Order Traversal of a Binary Tree

Problem Restatement We are given the root of a binary tree. Each node has a coordinate: Node Position Root (row = 0, col = 0) Left child (row + 1, col - 1) Right child (row + 1, col + 1) We need to return the vertical order traversal of the tree. That means: Visit columns from left to right. Inside each column, visit nodes from top to bottom. If...

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LeetCode 863: All Nodes Distance K in Binary Tree

Problem Restatement We are given the root of a binary tree, a target node, and an integer k . We need to return the values of all nodes whose distance from the target node is exactly k . Distance means the number of edges on the path between two nodes. The answer can be returned in any order. Input and Output Item Meaning Input root , the root of the...

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LeetCode 958: Check Completeness of a Binary Tree

Problem Restatement We are given the root of a binary tree. We need to determine whether the tree is a complete binary tree. A complete binary tree has these properties: Every level except possibly the last is completely filled. All nodes in the last level are as far left as possible. Return true if the tree is complete. Otherwise, return false . The official problem states this exact definition: every...

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LeetCode 671: Second Minimum Node In a Binary Tree

Problem Restatement We are given a non-empty special binary tree. The tree has these rules: Rule Meaning Children count Each node has either 0 or 2 children Parent value If a node has children, its value is the smaller value among its two children Goal Find the second minimum value in the whole tree If no second minimum value exists, return -1 . Because each parent stores the smaller value...

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LeetCode 669: Trim a Binary Search Tree

Problem Restatement We are given the root of a binary search tree and two boundaries: Variable Meaning low Lowest allowed node value high Highest allowed node value We need to trim the tree so that every remaining node value lies inside: [low, high] The relative structure of the remaining nodes must stay the same. If one remaining node was a descendant of another remaining node before trimming, it should still...

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LeetCode 687: Longest Univalue Path

Problem Restatement We are given the root of a binary tree. We need to return the length of the longest path where every node on the path has the same value. The path may or may not pass through the root. The length of a path is counted by number of edges, not number of nodes. The official constraints allow an empty tree, up to 10^4 nodes, node values from...

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LeetCode 637: Average of Levels in Binary Tree

Problem Restatement We are given the root of a binary tree. We need to return an array where each element is the average value of all nodes on one level of the tree. The first value is the average of the root level. The second value is the average of the next level. The result continues from top to bottom. Answers within 10^-5 of the actual answer are accepted. The...

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LeetCode 617: Merge Two Binary Trees

Problem Restatement We are given two binary trees: root1 and root2 . We need to merge them into a single binary tree. The merge rule is: Case Result Both nodes exist Sum their values One node is null Use the non-null node Both null Result is null We return the merged tree as the new root. The official problem defines merging two binary trees by summing overlapping nodes and using...

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LeetCode 666: Path Sum IV

Problem Restatement We are given an array nums . Each integer in nums has exactly three digits and represents one node in a binary tree. For a number DPV : Digit Meaning D Depth of the node P Position of the node within that depth V Value of the node Depth and position are 1-based. The tree depth is less than 5 , so valid depths are from 1 to...

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LeetCode 663: Equal Tree Partition

Problem Restatement We are given the root of a binary tree. We need to decide whether we can remove exactly one edge so that the tree is split into two smaller trees with equal sums. Each tree sum is the sum of all node values inside that tree. Return True if such an edge exists. Otherwise, return False . Input and Output Item Meaning Input The root of a binary...

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LeetCode 979: Distribute Coins in Binary Tree

Problem Restatement We are given the root of a binary tree with n nodes. Each node has some number of coins stored in node.val . There are exactly n coins total in the whole tree, so it is possible for every node to end with exactly one coin. In one move, we may move one coin between two adjacent nodes. Adjacent means parent and child. We need to return the...

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LeetCode 662: Maximum Width of Binary Tree

Problem Restatement We are given the root of a binary tree. We need to return the maximum width among all levels of the tree. The width of a level is measured between the leftmost and rightmost non-null nodes on that level. However, null nodes between those two endpoints are also counted, as if the tree were placed inside a complete binary tree. Input and Output Item Meaning Input The root...

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LeetCode 549: Binary Tree Longest Consecutive Sequence II

Problem Restatement We are given the root of a binary tree. We need to find the length of the longest consecutive path. A path can move from parent to child or child to parent, as long as the path stays connected. The consecutive values may either: increase by 1 decrease by 1 The path may change direction once at a node. For example: 1 - 2 - 3 is valid...

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LeetCode 606: Construct String from Binary Tree

Problem Restatement We are given the root of a binary tree. We need to convert the tree into a string using preorder traversal: Step Meaning Visit current node Output node value Visit left subtree Wrap in parentheses Visit right subtree Wrap in parentheses However, unnecessary empty parentheses should be omitted. There is one important exception: If a node has a right child but no left child, we must include: ()...

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LeetCode 572: Subtree of Another Tree

Problem Restatement We are given the roots of two binary trees: Name Meaning root The larger tree subRoot The tree we want to find inside root Return True if there is a subtree of root that has exactly the same structure and node values as subRoot . A subtree means a node and all of its descendants. A tree is also considered a subtree of itself. The official constraints say...

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LeetCode 545: Boundary of Binary Tree

Problem Restatement We are given the root of a binary tree. We need to return the boundary of the tree in anti-clockwise order starting from the root. The boundary consists of three parts: Left boundary Leaf nodes Right boundary in reverse order There are important rules: Part Rule Root Included once Left boundary Exclude leaves Leaves Include all leaves from left to right Right boundary Exclude leaves and reverse order...

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LeetCode 543: Diameter of Binary Tree

Problem Restatement We are given the root of a binary tree. We need to return the length of the tree's diameter. The diameter is the length of the longest path between any two nodes in the tree. This path may or may not pass through the root. The length is measured by the number of edges, not the number of nodes. For example, in root = [1,2,3,4,5] , one longest...

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LeetCode 515: Find Largest Value in Each Tree Row

Problem Restatement We are given the root of a binary tree. For every depth level in the tree, we need to find the largest node value on that row. Return the results as an array where: answer[i] is the maximum value on depth i . The official problem asks us to return the largest value in each row of a binary tree. Input and Output Item Meaning Input The root...

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LeetCode 513: Find Bottom Left Tree Value

Problem Restatement We are given the root of a binary tree. We need to return the leftmost value in the last row of the tree. The last row means the deepest level of the tree. The leftmost value means the first node on that deepest level when reading from left to right. The official problem asks us to return the leftmost value in the last row of a binary tree....

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LeetCode 508: Most Frequent Subtree Sum

Problem Restatement We are given the root of a binary tree. For every node, define its subtree sum as the sum of all values in the subtree rooted at that node. This includes the node itself and all of its descendants. We need to return the subtree sum value or values that appear most frequently. If several subtree sums have the same highest frequency, return all of them in any...

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LeetCode 655: Print Binary Tree

Problem Restatement We are given the root of a binary tree. We need to return a 2D string matrix that represents the tree in a formatted layout. The layout follows fixed rules: Rule Meaning Rows One row for each tree level Columns Enough columns to center every subtree Root placement The root goes in the middle of the first row Child placement Children are placed one row below their parent...

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LeetCode 563: Binary Tree Tilt

Problem Restatement We are given the root of a binary tree. For each node, its tilt is the absolute difference between: Side Meaning Left subtree sum Sum of all values in the left subtree Right subtree sum Sum of all values in the right subtree If a node has no left child, its left subtree sum is 0 . If a node has no right child, its right subtree sum...

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LeetCode 654: Maximum Binary Tree

Problem Restatement We are given an array of distinct integers called nums . We must construct a binary tree using the following rules: The root is the maximum number in the array. The left subtree is built recursively from the elements to the left of the maximum number. The right subtree is built recursively from the elements to the right of the maximum number. Return the root of the constructed...

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LeetCode 653: Two Sum IV - Input is a BST

Problem Restatement We are given the root of a binary search tree and an integer k . We need to return True if there are two different nodes in the tree whose values add up to k . Otherwise, return False . The two values must come from two different nodes. We cannot use the same node twice. Input and Output Item Meaning Input The root of a binary search...

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LeetCode 951: Flip Equivalent Binary Trees

Problem Restatement We are given the roots of two binary trees, root1 and root2 . A flip operation chooses one node and swaps its left and right child subtrees. Two trees are flip equivalent if we can make them equal after doing zero or more flip operations. Return true if the two trees are flip equivalent. Otherwise, return false . The official constraints say each tree has between 0 and...

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LeetCode 701: Insert into a Binary Search Tree

Problem Restatement We are given the root of a binary search tree and a value val . We need to insert val into the tree while keeping the binary search tree property valid. A binary search tree has this rule: Position Rule Left subtree Values are smaller than the current node Right subtree Values are greater than the current node The problem guarantees that val does not already exist in...

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LeetCode 652: Find Duplicate Subtrees

Problem Restatement We are given the root of a binary tree. We need to find all duplicate subtrees. Two subtrees are duplicate when they have: Requirement Meaning Same structure The nodes are arranged in the same shape Same values Matching nodes have equal values For each kind of duplicate subtree, we only return one root node. For example, if the same subtree appears three times, we still add only one...

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LeetCode 501: Find Mode in Binary Search Tree

Problem Restatement We are given the root of a binary search tree that may contain duplicate values. We need to return all values that appear most frequently in the tree. A value with the highest frequency is called a mode. If more than one value has the same highest frequency, return all of them in any order. The official statement defines the input as a BST with duplicates and asks...

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LeetCode 536: Construct Binary Tree from String

Problem Restatement We are given a string representing a binary tree. The string format is: node(left_subtree)(right_subtree) Each node starts with an integer value. If a node has children, the left subtree appears first inside parentheses. The right subtree appears second inside another pair of parentheses. We need to reconstruct the binary tree and return its root. The string may contain negative integers. Input and Output Item Meaning Input A string...

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LeetCode 298: Binary Tree Longest Consecutive Sequence

Problem Restatement We are given the root of a binary tree. We need to return the length of the longest consecutive sequence path. A consecutive path means each next node has value exactly one greater than its parent. For example: 3 -> 4 -> 5 is valid. But: 3 -> 2 -> 1 is not valid, because the values decrease. The path can start at any node, but it must...

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LeetCode 297: Serialize and Deserialize Binary Tree

Problem Restatement We need to design a codec for a binary tree. The codec has two operations: serialize(root) deserialize(data) serialize(root) converts a binary tree into a string. deserialize(data) converts that string back into the original binary tree. There is no required string format. The only requirement is that a tree serialized by our method can be deserialized back into the same tree structure. The source statement also clarifies that we...

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LeetCode 366: Find Leaves of Binary Tree

Problem Restatement We are given the root of a binary tree. We need to collect the tree's nodes as if we repeatedly do this: Collect all current leaf nodes. Remove those leaf nodes. Repeat until the tree is empty. Return a list of lists. Each inner list contains the node values removed in the same round. The order inside each round does not matter. The official example is: root =...

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LeetCode 222: Count Complete Tree Nodes

Problem Restatement We are given the root of a complete binary tree. We need to return the number of nodes in the tree. A complete binary tree has this shape: Rule Meaning Every level except possibly the last Completely filled Last level Filled from left to right Missing nodes Can only appear at the far right of the last level The official problem asks for an algorithm that runs in...

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LeetCode 100: Same Tree

Problem Restatement We are given the roots of two binary trees: p q We need to check whether the two trees are the same. Two binary trees are the same if: Requirement Meaning Same structure Every node position exists in both trees or in neither tree Same values Corresponding nodes have equal values The official statement defines two binary trees as the same when they are structurally identical and their...

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LeetCode 124: Binary Tree Maximum Path Sum

Problem Restatement We are given the root of a binary tree. We need to find the maximum path sum of any non-empty path in the tree. A path is a sequence of connected nodes where each pair of adjacent nodes has an edge between them. A node may appear in the path at most once. The path does not need to pass through the root. The official problem asks for...

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LeetCode 94: Binary Tree Inorder Traversal

Problem Restatement We are given the root of a binary tree. We need to return the inorder traversal of the tree's node values. Inorder traversal means: left subtree current node right subtree The official constraints say the number of nodes is between 0 and 100 , and each node value is between -100 and 100 . The follow-up asks for an iterative solution. Input and Output Item Meaning Input Root...

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LeetCode 145: Binary Tree Postorder Traversal

Problem Restatement We are given the root of a binary tree. Return the postorder traversal of its node values. Postorder traversal visits nodes in this order: left subtree -> right subtree -> root If the tree is empty, return an empty list. LeetCode also includes a follow-up asking for an iterative solution. Examples Example 1: 1 \ 2 / 3 Traversal order: visit left of 1: none visit right subtree...

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LeetCode 144: Binary Tree Preorder Traversal

Problem Restatement We are given the root of a binary tree. Return the preorder traversal of its node values. Preorder traversal visits nodes in this order: root -> left subtree -> right subtree The tree may be empty. In that case, return an empty list. LeetCode also includes a follow-up asking for an iterative solution. Examples Example 1: 1 \ 2 / 3 Preorder traversal: visit 1 go right to...

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LeetCode 199: Binary Tree Right Side View

Problem Restatement We are given the root of a binary tree. Imagine standing on the right side of the tree. From that view, at each depth, only the rightmost node is visible. We need to return the visible node values from top to bottom. The official problem asks for the values of nodes visible from the right side of the binary tree. Input and Output Item Meaning Input Root of...

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LeetCode 117: Populating Next Right Pointers in Each Node II

Problem Restatement We are given the root of a binary tree. Each node has four fields: val left right next We must populate every next pointer so that it points to the next node on the same level. If there is no node to the right, the next pointer should be None . Unlike LeetCode 116, the tree is not necessarily perfect. Some nodes may have only one child or...

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LeetCode 116: Populating Next Right Pointers in Each Node

Problem Restatement We are given a perfect binary tree. A perfect binary tree has two important properties: Every internal node has exactly two children. All leaves are on the same level. Each node has four fields: val left right next We need to populate each next pointer so that it points to the node immediately to its right on the same level. If there is no node to the right,...

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LeetCode 114: Flatten Binary Tree to Linked List

Problem Restatement We are given the root of a binary tree. We need to flatten the tree into a linked list in-place. The linked list must follow the same order as preorder traversal: root -> left -> right After flattening: Every node's left child must become None . Every node's right child points to the next node in preorder order. The official problem specifically requires the flattened structure to use...

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LeetCode 113: Path Sum II

Problem Restatement We are given the root of a binary tree and an integer targetSum . We need to return all root-to-leaf paths where the sum of node values equals targetSum . Each returned path must: Start at the root. End at a leaf. Have node values summing to targetSum . The official problem asks for all root-to-leaf paths whose sum equals the target. For this tree: 5 / \...

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LeetCode 112: Path Sum

Problem Restatement We are given the root of a binary tree and an integer targetSum . We need to return True if the tree has at least one root-to-leaf path whose node values add up to targetSum . A leaf is a node with no children. If no such path exists, return False . The official problem uses this same root-to-leaf path requirement. For this tree: 5 / \ 4...

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LeetCode 111: Minimum Depth of Binary Tree

Problem Restatement We are given the root of a binary tree. We need to return its minimum depth. The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node. A leaf is a node with no children. For this tree: 3 / \ 9 20 / \ 15 7 The nearest leaf is 9 . The path is: 3...

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LeetCode 110: Balanced Binary Tree

Problem Restatement We are given the root of a binary tree. We need to determine whether the tree is height-balanced. A binary tree is height-balanced when the left and right subtrees of every node differ in height by no more than 1 . The official problem asks us to return true if the tree is balanced, otherwise false . For this tree: 3 / \ 9 20 / \ 15...

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LeetCode 314: Binary Tree Vertical Order Traversal

Problem Restatement We are given the root of a binary tree. Return the vertical order traversal of the tree's node values. Vertical order means: Group nodes by column. Output columns from left to right. Inside each column, output nodes from top to bottom. If two nodes have the same row and column, output the left node before the right node. The root starts at column 0 . For any node:...

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LeetCode 236: Lowest Common Ancestor of a Binary Tree

Problem Restatement We are given: The root of a binary tree Two nodes p and q We need to return their lowest common ancestor. The lowest common ancestor is the lowest node in the tree that has both p and q as descendants. A node can be a descendant of itself. Unlike LeetCode 235, this tree is a normal binary tree, not a binary search tree. So we cannot use...

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LeetCode 107: Binary Tree Level Order Traversal II

Problem Restatement We are given the root of a binary tree. We need to return the node values level by level, but from bottom to top. Inside each level, values must still be ordered from left to right. The official problem asks for the bottom-up level order traversal of the binary tree's node values, from leaf level to root level. For this tree: 3 / \ 9 20 / \...

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LeetCode 437: Path Sum III

Problem Restatement We are given the root of a binary tree and an integer targetSum . We need to count how many paths have node values that add up to targetSum . A valid path: Rule Meaning Can start anywhere It does not have to start at the root Can end anywhere It does not have to end at a leaf Must go downward It can only move from parent...

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LeetCode 337: House Robber III

Problem Restatement We are given the root of a binary tree. Each node represents a house, and the value of the node is the amount of money in that house. A thief wants to rob houses, but there is one rule: If two directly connected houses are robbed, the police are alerted. In tree terms, we cannot rob both a parent node and its child node. Return the maximum amount...

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LeetCode 106: Construct Binary Tree from Inorder and Postorder Traversal

Problem Restatement We are given two integer arrays: inorder postorder Both arrays describe the same binary tree. inorder is the inorder traversal of the tree. postorder is the postorder traversal of the same tree. We need to construct and return the original binary tree. The values are unique, and both arrays are guaranteed to describe the same tree. The official constraints also say each value in postorder appears in inorder...

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LeetCode 105: Construct Binary Tree from Preorder and Inorder Traversal

Problem Restatement We are given two integer arrays: preorder inorder Both arrays describe the same binary tree. preorder is the preorder traversal of the tree. inorder is the inorder traversal of the same tree. We need to construct and return the original binary tree. The official problem states that preorder and inorder are traversals of the same tree. The key traversal rules are: preorder: root -> left -> right inorder:...

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LeetCode 257: Binary Tree Paths

Problem Restatement We are given the root of a binary tree. We need to return all paths from the root to every leaf node. A leaf node is a node with no left child and no right child. Each path must be returned as a string using "->" between node values. For example, this path: 1 \ 2 \ 5 becomes: "1->2->5" The problem asks for all root-to-leaf paths in...

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LeetCode 104: Maximum Depth of Binary Tree

Problem Restatement We are given the root of a binary tree. We need to return its maximum depth. The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node. The official statement uses this same definition. For this tree: 3 / \ 9 20 / \ 15 7 The longest root-to-leaf path is: 3 -> 20 -> 15 or:...

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LeetCode 404: Sum of Left Leaves

Problem Restatement We are given the root of a binary tree. A leaf node is a node with no children: node.left is None and node.right is None A left leaf is a leaf node that is also the left child of its parent. We must return the sum of all left leaves in the tree. Input and Output Item Meaning Input The root of a binary tree Output The sum...

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LeetCode 103: Binary Tree Zigzag Level Order Traversal

Problem Restatement We are given the root of a binary tree. We need to return the values level by level. The first level is read from left to right, the second level from right to left, the third level from left to right, and so on. The official problem asks for the zigzag level order traversal of a binary tree's node values. For this tree: 3 / \ 9 20...

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LeetCode 431: Encode N-ary Tree to Binary Tree

Problem Restatement We need to design a way to convert an N-ary tree into a binary tree and then reconstruct the original N-ary tree. Two methods are required: Method Meaning encode(root) Convert an N-ary tree into a binary tree decode(root) Convert the binary tree back into the original N-ary tree The conversion must preserve the full tree structure. An N-ary tree node can have any number of children. A binary...

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LeetCode 156: Binary Tree Upside Down

Problem Restatement We are given the root of a binary tree. We need to flip the tree upside down and return the new root. The transformation follows these rules: The original left child becomes the new root of that local subtree. The original root becomes the new right child. The original right child becomes the new left child. The operation is done level by level. The input has an important...

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LeetCode 331: Verify Preorder Serialization of a Binary Tree

Problem Restatement We are given a string preorder . The string represents a preorder traversal serialization of a binary tree. Each token is separated by a comma. A non-null node is written as an integer. A null child is written as # . For example: "9,3,4,#,#,1,#,#,2,#,6,#,#" We need to return true if this string is a valid preorder serialization of some binary tree. We are not allowed to reconstruct the...

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LeetCode 129: Sum Root to Leaf Numbers

Problem Restatement We are given the root of a binary tree. Each node contains a digit from 0 to 9 . Every root-to-leaf path represents one number. For example, the path 1 -> 2 -> 3 represents the number 123 . We need to return the sum of all numbers formed by all root-to-leaf paths. A leaf is a node with no children. The answer is guaranteed to fit in...

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LeetCode 102: Binary Tree Level Order Traversal

Problem Restatement We are given the root of a binary tree. We need to return the node values level by level, from left to right inside each level. The official problem asks for the level order traversal of the binary tree's node values. For this tree: 3 / \ 9 20 / \ 15 7 The answer is: [[3], [9, 20], [15, 7]] Each inner list contains one tree level....

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LeetCode 226: Invert Binary Tree

Problem Restatement We are given the root of a binary tree. We need to invert the tree and return its root. Inverting means every node swaps its left child and right child. For example, LeetCode gives this input and output: root = [4,2,7,1,3,6,9] becomes [4,7,2,9,6,3,1] . The constraints say the tree has between 0 and 100 nodes, and each node value is between -100 and 100 . Input and Output...

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LeetCode 101: Symmetric Tree

Problem Restatement We are given the root of a binary tree. We need to check whether the tree is symmetric around its center. In other words, the left subtree must be a mirror image of the right subtree. The official problem asks whether the binary tree is a mirror of itself. A tree like this is symmetric: 1 / \ 2 2 / \ / \ 3 4 4 3...

#binary-tree

LeetCode 3831 - Median of a Binary Search Tree Level

LeetCode 3526 - Range XOR Queries with Subarray Reversals

LeetCode 3879 - Maximum Distinct Path Sum in a Binary Tree

LeetCode 2509 - Cycle Length Queries in a Tree

LeetCode 2458 - Height of Binary Tree After Subtree Removal Queries

LeetCode 2049 - Count Nodes With the Highest Score

LeetCode 2792 - Count Nodes That Are Great Enough

LeetCode 2471 - Minimum Number of Operations to Sort a Binary Tree by Level

LeetCode 2773 - Height of Special Binary Tree

LeetCode 2313 - Minimum Flips in Binary Tree to Get Result

LeetCode 2096 - Step-By-Step Directions From a Binary Tree Node to Another

LeetCode 3319 - K-th Largest Perfect Subtree Size in Binary Tree

LeetCode 2331 - Evaluate Boolean Binary Tree

LeetCode 2415 - Reverse Odd Levels of Binary Tree

LeetCode 1932 - Merge BSTs to Create Single BST

LeetCode 2583 - Kth Largest Sum in a Binary Tree

LeetCode 2689 - Extract Kth Character From The Rope Tree

LeetCode 2265 - Count Nodes Equal to Average of Subtree

LeetCode 2641 - Cousins in Binary Tree II

LeetCode 2764 - Is Array a Preorder of Some ‌Binary Tree

LeetCode 2385 - Amount of Time for Binary Tree to Be Infected

LeetCode 2196 - Create Binary Tree From Descriptions

LeetCode 2445 - Number of Nodes With Value One

LeetCode 3157 - Find the Level of Tree with Minimum Sum

LeetCode 1902 - Depth of BST Given Insertion Order

LeetCode 2476 - Closest Nodes Queries in a Binary Search Tree

LeetCode 1973 - Count Nodes Equal to Sum of Descendants

LeetCode 2673 - Make Costs of Paths Equal in a Binary Tree

LeetCode 2236 - Root Equals Sum of Children

LeetCode 101 - Symmetric Tree

LeetCode 144 - Binary Tree Preorder Traversal

LeetCode 331 - Verify Preorder Serialization of a Binary Tree

LeetCode 107 - Binary Tree Level Order Traversal II

LeetCode 117 - Populating Next Right Pointers in Each Node II

LeetCode 1302 - Deepest Leaves Sum

LeetCode 897 - Increasing Order Search Tree

LeetCode 145 - Binary Tree Postorder Traversal

LeetCode 404 - Sum of Left Leaves

LeetCode 958 - Check Completeness of a Binary Tree

LeetCode 1026 - Maximum Difference Between Node and Ancestor

LeetCode 1485 - Clone Binary Tree With Random Pointer

LeetCode 1612 - Check If Two Expression Trees are Equivalent

LeetCode 971 - Flip Binary Tree To Match Preorder Traversal

LeetCode 366 - Find Leaves of Binary Tree

LeetCode 100 - Same Tree

LeetCode 250 - Count Univalue Subtrees

LeetCode 1530 - Number of Good Leaf Nodes Pairs

LeetCode 617 - Merge Two Binary Trees

LeetCode 450 - Delete Node in a BST

LeetCode 938 - Range Sum of BST

LeetCode 652 - Find Duplicate Subtrees

LeetCode 426 - Convert Binary Search Tree to Sorted Doubly Linked List

LeetCode 98 - Validate Binary Search Tree

LeetCode 314 - Binary Tree Vertical Order Traversal

LeetCode 606 - Construct String from Binary Tree

LeetCode 536 - Construct Binary Tree from String

LeetCode 666 - Path Sum IV

LeetCode 1028 - Recover a Tree From Preorder Traversal

LeetCode 1740 - Find Distance in a Binary Tree

LeetCode 1469 - Find All The Lonely Nodes

LeetCode 230 - Kth Smallest Element in a BST

LeetCode 655 - Print Binary Tree

LeetCode 1110 - Delete Nodes And Return Forest

LeetCode 1315 - Sum of Nodes with Even-Valued Grandparent

LeetCode 124 - Binary Tree Maximum Path Sum

LeetCode 104 - Maximum Depth of Binary Tree

LeetCode 1367 - Linked List in Binary Tree

LeetCode 965 - Univalued Binary Tree

LeetCode 99 - Recover Binary Search Tree

LeetCode 333 - Largest BST Subtree

LeetCode 108 - Convert Sorted Array to Binary Search Tree

LeetCode 173 - Binary Search Tree Iterator

LeetCode 129 - Sum Root to Leaf Numbers

LeetCode 1609 - Even Odd Tree

LeetCode 1448 - Count Good Nodes in Binary Tree

LeetCode 1022 - Sum of Root To Leaf Binary Numbers

LeetCode 513 - Find Bottom Left Tree Value

LeetCode 1305 - All Elements in Two Binary Search Trees

LeetCode 110 - Balanced Binary Tree