LeetCode Solutions

Computer science is no more about computers than astronomy is about telescopes. — E. W. Dijkstra

Contents

• LeetCode Solutions
  • Contents
  • Directory Structure
  • Essential Algorithm Fundamentals
    • Algorithm Basics You Must Master:
    • Core Algorithm Ideas:
  • Must-Know Classic LeetCode Problems by Category
  • Visualization Algorithm Tools
  • Algorithm Learning Resources
  • Todo List

Welcome! This repository contains my solutions to LeetCode problems, implemented in Go and Python.

Each problem is organized by language and directory. Solutions include clean code, unit tests, and concise explanations where appropriate.

Directory Structure

• 📂 go/ — Go solutions
• 📂 python/ — Python solutions

Feel free to explore, learn, and discuss. Contributions and suggestions are always welcome!

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Essential Algorithm Fundamentals

Algorithm Basics You Must Master:

1. Linked List: traversal, reversal, merging, cycle detection
2. Binary Tree: level order(max/min depth, symmetric tree), preorder/inorder/postorder traversal (both recursive and iterative), inversion, lowest common ancestor, merge two binary trees
3. Sorting: quick sort, merge sort, insertion sort, selection sort, bubble sort, heap sort
4. Binary Search: on sorted arrays, binary trees
5. Bit Manipulation Techniques:
   • XOR (^): find numbers that appear only once or twice.
   • AND (&):
     • n & (n-1): removes the lowest set bit, commonly used to check if a number is a power of 2.
     • n & -n: gets the lowest set bit.
   • << and >>: efficient multiplication and division by 2.
   • Use XOR to find the unique unpaired number.
6. Math Techniques: fast exponentiation, GCD/LCM, elementary math simulation

Core Algorithm Ideas:

1. Hash table: trading space for time
2. Two pointers: fast/slow pointers, left/right pointers (collision pointers), sliding window
3. DFS: using a stack
4. BFS/backtracking: using a queue
5. Dynamic Programming (DP)

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Must-Know Classic LeetCode Problems by Category

1. Arrays & Strings

• 1. Two Sum
• 121. Best Time to Buy and Sell Stock
• 189. Rotate Array
• 217. Contains Duplicate
• 238. Product of Array Except Self
• 3. Longest Substring Without Repeating Characters
• 125. Valid Palindrome

2. Linked Lists

• 206. Reverse Linked List
• 21. Merge Two Sorted Lists
• 141. Linked List Cycle
• 19. Remove Nth Node From End of List
• 234. Palindrome Linked List

3. Stacks & Queues

• 20. Valid Parentheses
• 155. Min Stack
• 739. Daily Temperatures
• 232. Implement Queue using Stacks

4. Hash Tables

• 1. Two Sum
• 49. Group Anagrams
• 349. Intersection of Two Arrays
• 146. LRU Cache

5. Binary Search

• 704. Binary Search
• 35. Search Insert Position
• 153. Find Minimum in Rotated Sorted Array
• 33. Search in Rotated Sorted Array

6. Dynamic Programming

• 70. Climbing Stairs
• 53. Maximum Subarray
• 322. Coin Change
• 300. Longest Increasing Subsequence
• 72. Edit Distance

7. Backtracking

• 78. Subsets
• 46. Permutations
• 39. Combination Sum
• 79. Word Search

8. Trees & Recursion

• 104. Maximum Depth of Binary Tree
• 226. Invert Binary Tree
• 101. Symmetric Tree
• 102. Binary Tree Level Order Traversal
• 235. Lowest Common Ancestor of a BST

9. Graphs (BFS & DFS)

• 200. Number of Islands
• 133. Clone Graph
• 207. Course Schedule
• 127. Word Ladder

10. Greedy Algorithms

• 55. Jump Game
• 455. Assign Cookies
• 435. Non-overlapping Intervals

11. Math & Bit Manipulation

• 231. Power of Two
• 69. Sqrt(x)
• 371. Sum of Two Integers

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Visualization Algorithm Tools

• Algorithm Visualizer
• VisuAlgo

Algorithm Learning Resources

• Hello 算法
• Labuladong 的算法笔记
• 代码随想录

Todo List

• 中英双语文档
• 每个题目分析平均、最好、最坏时间复杂度
• 每个题目分析不同解法的优缺点
• 使用 Python 求解