LeetCode Solutions

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

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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

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📄 License

This project is dual-licensed:

• Code (Go, Python, etc.): MIT License
• Documentation & Images: CC BY 4.0

Feel free to use, modify, and share this project. Attribution is appreciated! ❤️