LeetCode 965: Univalued Binary Tree
A clear explanation of checking whether every node in a binary tree has the same value.
Tag
Recursion
80 notes
LeetCode 951: Flip Equivalent Binary Trees
A clear explanation of checking whether two binary trees are equivalent after swapping left and right children at any number of nodes.
LeetCode 894: All Possible Full Binary Trees
A clear explanation of generating all full binary trees with n nodes using recursion and memoization.
LeetCode 250: Count Univalue Subtrees
A clear explanation of counting uni-value subtrees using post-order DFS.
LeetCode 248: Strobogrammatic Number III
A clear explanation of counting strobogrammatic numbers in a string range using recursive generation and range filtering.
LeetCode 247: Strobogrammatic Number II
A clear explanation of generating all strobogrammatic numbers of length n using recursion from the inside out.
LeetCode 998: Maximum Binary Tree II
A clear explanation of inserting a value into a maximum binary tree by following the right spine.
LeetCode 865: Smallest Subtree with all the Deepest Nodes
A clear explanation of finding the smallest subtree that contains all deepest nodes using bottom-up DFS.
LeetCode 814: Binary Tree Pruning
A postorder DFS solution for removing every binary tree subtree that does not contain a 1.
LeetCode 784: Letter Case Permutation
A clear explanation of generating all strings formed by independently changing each letter to lowercase or uppercase.
LeetCode 779: K-th Symbol in Grammar
A clear explanation of finding the kth symbol in the grammar sequence using recursion and the parent-child relationship.
LeetCode 776: Split BST
A clear explanation of splitting a binary search tree into two BSTs using recursion and pointer rewiring.
LeetCode 772: Basic Calculator III
A clear explanation of evaluating arithmetic expressions with parentheses, precedence, and integer division.
LeetCode 770: Basic Calculator IV
A clear explanation of simplifying algebraic expressions by parsing, substituting variables, and combining polynomial terms.
LeetCode 761: Special Binary String
A clear explanation of making a special binary string lexicographically largest using recursive decomposition and sorting.
LeetCode 701: Insert into a Binary Search Tree
A clear explanation of inserting a value into a binary search tree using recursive and iterative traversal.
LeetCode 736: Parse Lisp Expression
Evaluate a Lisp-like expression with integers, variables, let bindings, addition, multiplication, and lexical scope.
LeetCode 669: Trim a Binary Search Tree
A clear explanation of trimming a BST so that all remaining node values lie inside a given inclusive range.
LeetCode 655: Print Binary Tree
A clear explanation of formatting a binary tree into a 2D string matrix using tree height and recursive placement.
LeetCode 654: Maximum Binary Tree
A clear explanation of constructing a maximum binary tree recursively using divide and conquer.
LeetCode 631: Design Excel Sum Formula
A design solution for a small Excel-like spreadsheet that supports set, get, and dynamic sum formulas.
LeetCode 617: Merge Two Binary Trees
A recursive tree traversal guide for merging two binary trees node by node.
LeetCode 606: Construct String from Binary Tree
A recursive guide for converting a binary tree into a preorder parenthesized string while preserving the one-to-one mapping between the tree and the string.
LeetCode 241: Different Ways to Add Parentheses
A clear explanation of generating all possible results from different parenthesizations using divide and conquer recursion.
LeetCode 236: Lowest Common Ancestor of a Binary Tree
A clear explanation of finding the lowest common ancestor in a normal binary tree using recursive depth-first search.
LeetCode 234: Palindrome Linked List
A clear explanation of checking whether a singly linked list is a palindrome using fast and slow pointers plus in-place reversal.
LeetCode 226: Invert Binary Tree
A clear explanation of inverting a binary tree using recursive depth-first traversal.
LeetCode 50: Pow(x, n)
A clear explanation of Pow(x, n) using binary exponentiation to compute powers in logarithmic time.
LeetCode 687: Longest Univalue Path
Find the longest path in a binary tree where every node on the path has the same value using depth-first search.
LeetCode 590: N-ary Tree Postorder Traversal
A clear DFS solution for returning the postorder traversal of an N-ary tree.
LeetCode 589: N-ary Tree Preorder Traversal
A clear DFS solution for returning the preorder traversal of an N-ary tree.
LeetCode 572: Subtree of Another Tree
A clear explanation of Subtree of Another Tree using recursive tree matching and DFS.
LeetCode 546: Remove Boxes
A clear explanation of maximizing remove-box scores using interval dynamic programming with memoization.
LeetCode 544: Output Contest Matches
A clear explanation of building the final tournament bracket by repeatedly pairing strongest and weakest teams.
LeetCode 543: Diameter of Binary Tree
A clear explanation of finding the longest path between any two nodes in a binary tree using DFS height computation.
LeetCode 536: Construct Binary Tree from String
A clear explanation of parsing a parenthesized string recursively to construct a binary tree.
LeetCode 509: Fibonacci Number
A clear explanation of computing Fibonacci numbers using dynamic programming and iterative state transitions.
LeetCode 558: Logical OR of Two Binary Grids Represented as Quad-Trees
A clear explanation of merging two quad-trees using recursive logical OR operations.
LeetCode 486: Predict the Winner
A clear explanation of predicting whether Player 1 can win using minimax dynamic programming over score difference.
LeetCode 450: Delete Node in a BST
Delete a node from a binary search tree while preserving the BST property using recursive search and inorder successor replacement.
LeetCode 430: Flatten a Multilevel Doubly Linked List
Flatten a multilevel doubly linked list in-place using depth-first traversal and pointer splicing.
LeetCode 428: Serialize and Deserialize N-ary Tree
Serialize an N-ary tree into a string and reconstruct the same tree using preorder traversal with child counts.
LeetCode 427: Construct Quad Tree
Build a quad tree from a binary square grid using recursive divide and conquer.
LeetCode 404: Sum of Left Leaves
A clear explanation of the Sum of Left Leaves problem using depth-first traversal of a binary tree.
LeetCode 397: Integer Replacement
A clear explanation of reducing an integer to 1 with the fewest operations using greedy bit decisions.
LeetCode 394: Decode String
A clear explanation of decoding nested repeat expressions using a stack.
LeetCode 390: Elimination Game
A clear explanation of finding the last remaining number after alternating left-to-right and right-to-left eliminations.
LeetCode 372: Super Pow
A clear explanation of computing large modular exponentiation using fast power, modular arithmetic, and digit decomposition.
LeetCode 339: Nested List Weight Sum
A clear explanation of Nested List Weight Sum using depth-first search over a nested structure.
LeetCode 326: Power of Three
A clear explanation of the Power of Three problem using repeated division and integer arithmetic.
LeetCode 282: Expression Add Operators
A backtracking solution for inserting operators into a numeric string so the expression evaluates to a target value.
LeetCode 273: Integer to English Words
A clear explanation of the Integer to English Words problem using three-digit chunks and scale words.
LeetCode 222: Count Complete Tree Nodes
A clear explanation of counting nodes in a complete binary tree faster than visiting every node.
LeetCode 206: Reverse Linked List
A clear explanation of reversing a singly linked list using iterative and recursive approaches.
LeetCode 98: Validate Binary Search Tree
A detailed guide to solving Validate Binary Search Tree with recursive lower and upper bounds.
LeetCode 95: Unique Binary Search Trees II
A detailed guide to solving Unique Binary Search Trees II with recursive tree generation over value ranges.
LeetCode 94: Binary Tree Inorder Traversal
A detailed guide to solving Binary Tree Inorder Traversal with recursion and an iterative stack.
LeetCode 87: Scramble String
A detailed guide to solving Scramble String with recursive dynamic programming and memoization.
LeetCode 77: Combinations
A detailed guide to solving Combinations with backtracking and pruning.
LeetCode 156: Binary Tree Upside Down
A clear explanation of flipping a binary tree upside down by rewiring pointers from the left spine.
LeetCode 129: Sum Root to Leaf Numbers
Compute the sum of all numbers formed by root-to-leaf paths using depth-first search and decimal accumulation.
LeetCode 114: Flatten Binary Tree to Linked List
A clear explanation of flattening a binary tree into a linked list in preorder traversal order using recursive depth-first search.
LeetCode 113: Path Sum II
A clear explanation of finding all root-to-leaf paths whose values add up to a target sum using depth-first search and backtracking.
LeetCode 112: Path Sum
A clear explanation of checking whether a binary tree has a root-to-leaf path whose values add up to a target sum.
LeetCode 110: Balanced Binary Tree
A clear explanation of checking whether a binary tree is height-balanced using bottom-up depth-first search.
LeetCode 108: Convert Sorted Array to Binary Search Tree
A clear explanation of building a height-balanced binary search tree from a sorted array using divide and conquer.
LeetCode 106: Construct Binary Tree from Inorder and Postorder Traversal
A clear explanation of rebuilding a binary tree from inorder and postorder traversals using recursion and an index map.
LeetCode 105: Construct Binary Tree from Preorder and Inorder Traversal
A clear explanation of rebuilding a binary tree from preorder and inorder traversals using recursion and an index map.
LeetCode 104: Maximum Depth of Binary Tree
A clear explanation of finding the maximum depth of a binary tree using recursive depth-first search.
LeetCode 101: Symmetric Tree
A clear explanation of checking whether a binary tree is symmetric using mirror recursion.
LeetCode 60: Permutation Sequence
A clear guide to finding the kth permutation sequence using factorial blocks instead of generating all permutations.
LeetCode 25: Reverse Nodes in k-Group
A detailed explanation of reversing linked-list nodes in groups of k using pointer manipulation and constant extra space.
LeetCode 24: Swap Nodes in Pairs
A detailed explanation of swapping every two adjacent nodes in a linked list using pointer manipulation.
LeetCode 21: Merge Two Sorted Lists
A detailed explanation of merging two sorted linked lists using a dummy node and pointer splicing.
LeetCode 10: Regular Expression Matching
A detailed explanation of matching a full string against a simplified regular expression with dot and star using dynamic programming.
Recursive Linear Search
Linear search expressed recursively by reducing the problem size one element at a time.
Recursive Binary Search
Binary search implemented using recursion over a shrinking interval.
7.3 Induction and Recursion
Using base cases and step rules to prove statements about objects built recursively.
6.5 Recursion and Induction
Defining objects step by step and proving properties by following the same construction.
1.5 Recursion Invariants
Recursive algorithms replace loop structure with self-reference.