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LeetCode Study Note | Problem 200: Number of Islands

2025-05-17

LeetCode Study Note #Array# Depth-First Search#Breadth-First Search#Matrix#Union Find
🌊 Problem Summary You are given a 2D grid consisting of '1's (land) and '0's (water). An island is formed by connecting adjacent lands horizontally o
LeetCode Study Note | Problem 15: 3Sum

2025-05-15

LeetCode Study Note #Array#Two Pointers#Sorting
✨ Problem Description Given an integer array nums, return all the unique triplets [nums[i], nums[j], nums[k]] such that i ≠ j ≠ k, and nums[i] + nums[
LeetCode Study Note | Problem 283: Move Zeroes

2025-05-15

LeetCode Study Note #Two Pointers#Array
🧩 Problem Description Given an integer array nums, move all 0’s to the end of it while maintaining the relative order of the non-zero elements. Examp
LeetCode Study Note | Problem 128: Longest Consecutive Sequence

2025-05-13

LeetCode Study Note #Array#Hash Table#Union Find
📌 Problem Summary Given an unsorted array of integers, find the length of the longest consecutive elements sequence. Time complexity must be O(n). Ex
LeetCode Study Note | Problem 49: Group Anagrams

2025-05-13

LeetCode Study Note #Array#Hash Table#String#Sorting
🧩 Problem Summary Given an array of strings, group the anagrams together. Anagram: A word formed by rearranging the letters of another word (e.g., "e
LeetCode Study Note | Problem 2: Add Two Numbers

2025-05-12

LeetCode Study Note #Linked List#Math#Recursion
🧠 Problem Summary Given two non-empty linked lists representing two non-negative integers in reverse order (each node contains a single digit), retur
LeetCode Study Note | Problem 42: Trapping Rain Water

2025-05-11

LeetCode Study Note #Array#Two Pointers#Dynamic Programming#Stack
🔍 Problem Description Given a non-negative integer array height[] representing the elevation map where the width of each bar is 1, compute how much w
LeetCode Study Note | Problem 53: Maximum Subarray

2025-05-10

LeetCode Study Note #Array#Divide and Conquer#Dynamic Programming
Problem Overview Given an integer array nums, find the contiguous subarray (containing at least one number) which has the largest sum and return its s
LeetCode Study Note | Problem 3: Longest Substring Without Repeating Characters

2025-05-07

LeetCode Study Note #Hash Table#String#Sliding Window
Problem Overview Given a string s, find the length of the longest substring without repeating characters. Example： Input: "abcabcbb" Output: 3 Explana
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