LeetCode 835: Image Overlap
A clear explanation of the Image Overlap problem using translation vectors and frequency counting.
Tag
Hash-Map
55 notes
LeetCode 833: Find And Replace in String
A clear explanation of the Find And Replace in String problem using simultaneous replacement, source matching, and a replacement map.
LeetCode 828: Count Unique Characters of All Substrings of a Given String
A clear explanation of Count Unique Characters of All Substrings using contribution counting with previous and next occurrences.
LeetCode 621: Task Scheduler
A clear explanation of Task Scheduler using frequency counting and the greedy block formula.
LeetCode 249: Group Shifted Strings
A clear explanation of grouping strings by their shifting sequence using normalized hash keys.
LeetCode 246: Strobogrammatic Number
A clear explanation of the Strobogrammatic Number problem using digit rotation rules and two pointers.
LeetCode 244: Shortest Word Distance II
A clear explanation of the Shortest Word Distance II problem using preprocessing and two pointers.
LeetCode 940: Distinct Subsequences II
A clear explanation of solving Distinct Subsequences II using dynamic programming and last occurrence tracking.
LeetCode 930: Binary Subarrays With Sum
A clear explanation of solving Binary Subarrays With Sum using prefix sums and a frequency map.
LeetCode 823: Binary Trees With Factors
A dynamic programming solution for counting binary trees where every non-leaf node is the product of its children.
LeetCode 819: Most Common Word
A hash map and string parsing solution for finding the most frequent non-banned word in a paragraph.
LeetCode 815: Bus Routes
A BFS solution for finding the minimum number of buses needed to travel from a source stop to a target stop.
LeetCode 811: Subdomain Visit Count
A hash map solution for accumulating visit counts across domains and all of their parent subdomains.
LeetCode 792: Number of Matching Subsequences
A clear explanation of counting how many words are subsequences of a string using waiting queues.
LeetCode 791: Custom Sort String
A clear explanation of rearranging a string so that selected characters follow a custom order.
LeetCode 781: Rabbits in Forest
A clear explanation of finding the minimum possible number of rabbits using counting and greedy grouping.
LeetCode 726: Number of Atoms
Parse a chemical formula with nested parentheses, atom names, and multipliers using recursive descent.
LeetCode 697: Degree of an Array
Find the shortest contiguous subarray with the same degree as the whole array using frequency counts and first occurrence indices.
LeetCode 692: Top K Frequent Words
Find the k most frequent words using frequency counting and custom sorting by count and lexicographical order.
LeetCode 690: Employee Importance
Compute the total importance of an employee and all direct and indirect subordinates using a hash map and depth-first search.
LeetCode 677: Map Sum Pairs
Design a map that supports key-value insertion and prefix-sum queries using a hash map and trie.
LeetCode 676: Implement Magic Dictionary
Design a dictionary that can check whether a word can match a stored word after changing exactly one character.
LeetCode 666: Path Sum IV
A clear explanation of computing all root-to-leaf path sums from a compact three-digit binary tree encoding.
LeetCode 659: Split Array into Consecutive Subsequences
A clear explanation of deciding whether a sorted array can be split into consecutive subsequences of length at least three.
LeetCode 652: Find Duplicate Subtrees
A clear explanation of finding duplicate binary tree subtrees using postorder traversal, serialization, and a hash map.
LeetCode 642: Design Search Autocomplete System
A trie-based design for returning the top three historical sentences for a typed prefix.
LeetCode 631: Design Excel Sum Formula
A design solution for a small Excel-like spreadsheet that supports set, get, and dynamic sum formulas.
LeetCode 599: Minimum Index Sum of Two Lists
A clear hash map solution for finding common strings with the smallest index sum.
LeetCode 594: Longest Harmonious Subsequence
A clear hash map solution for finding the longest subsequence whose maximum and minimum differ by exactly one.
LeetCode 588: Design In-Memory File System
A clear design guide for implementing an in-memory file system with directory listing, directory creation, file append, and file read operations.
LeetCode 582: Kill Process
A clear graph traversal solution for finding all processes terminated when killing a target process.
LeetCode 567: Permutation in String
A clear explanation of Permutation in String using a fixed-size sliding window and character frequency counts.
LeetCode 560: Subarray Sum Equals K
A clear explanation of Subarray Sum Equals K using prefix sums and a hash map to count matching subarrays in linear time.
LeetCode 554: Brick Wall
A clear explanation of Brick Wall using prefix sums and a hash map to find the best vertical cut position.
LeetCode 525: Contiguous Array
A clear explanation of finding the longest contiguous subarray with equal numbers of 0 and 1 using prefix sums and a hash map.
LeetCode 523: Continuous Subarray Sum
A clear explanation of detecting a subarray whose sum is a multiple of k using prefix sums and modular arithmetic.
LeetCode 519: Random Flip Matrix
A clear explanation of randomly flipping zero cells in a matrix without repetition using hash mapping and virtual swapping.
LeetCode 508: Most Frequent Subtree Sum
A clear explanation of finding the most frequent subtree sum in a binary tree using postorder DFS and a frequency map.
LeetCode 506: Relative Ranks
A clear explanation of assigning athlete ranks from scores using sorting while preserving original indices.
LeetCode 465: Optimal Account Balancing
A clear explanation of minimizing debt-settlement transactions using net balances, backtracking, and memoization-style pruning.
LeetCode 460: LFU Cache
A clear explanation of designing an LFU cache with O(1) average get and put operations.
LeetCode 454: 4Sum II
A clear explanation of counting zero-sum tuples across four arrays using pair sums and a hash map.
LeetCode 451: Sort Characters By Frequency
A clear explanation of sorting characters by decreasing frequency using a hash map and sorting.
LeetCode 220: Contains Duplicate III
A clear explanation of checking nearby indices with nearby values using a sliding window and bucket hashing.
LeetCode 219: Contains Duplicate II
A clear explanation of detecting whether equal values appear within distance k using a hash map or sliding window set.
LeetCode 205: Isomorphic Strings
A clear explanation of checking whether two strings follow the same character mapping pattern.
LeetCode 76: Minimum Window Substring
A detailed guide to solving Minimum Window Substring with a sliding window and frequency counters.
LeetCode 149: Max Points on a Line
Find the maximum number of points lying on the same straight line using slope counting and normalization.
LeetCode 146: LRU Cache
Design an LRU cache with O(1) get and put operations using a hash map and doubly linked list.
LeetCode 138: Copy List with Random Pointer
Create a deep copy of a linked list with next and random pointers using hash maps or interleaved node cloning.
LeetCode 133: Clone Graph
Create a deep copy of a connected undirected graph using DFS and a hash map from original nodes to cloned nodes.
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 1: Two Sum
A clear explanation of the Two Sum problem using brute force first, then an optimized hash map solution.
Sparse Array
Store only non-default values from a large logical array.