Cpp and Python Solution for Leetcode with Basic idea. And the specific method is described in the first solution.
| Title | Solution | Difficulty | Basic idea |
|---|---|---|---|
| 1. Two Sum | Python | Easy | 1. two-pointer 2. hashtable |
| 7. Reverse Integer:star: | Python | Easy | 1. mod and floor divide in Python3 |
| 12. Integer to Roman | Python | Medium | decode mapping with greedy thinking |
| 13. Roman to Integer | Python | Easy | string traversal |
| 20. Valid Parentheses | Cpp Python | Easy | stack |
| 24. Swap Nodes in Pairs | Cpp | Medium | recursion |
| 26. Remove Duplicates from Sorted Array | Python | Easy | double pointer |
| 27. Remove Element | Python | Easy | double pointer |
| 28. Implement strStr() | Python | Easy | double pointer |
| 33. Search in Rotated Sorted Array | Python | Medium | binary search |
| 53. Maximum Subarray | Python | Easy | DP |
| 70. Climbing Stairs | Python | Easy | DP, recursive |
| 80. Remove Duplicates from Sorted Array II | Python | Medium | two pointer |
| 81. Search in Rotated Sorted Array II | Python | Medium | binary search |
| 88. Merge Sorted Array | Python | Easy | two pointer, reverse insertion |
| 91. Decode Ways | Python | Medium | DP |
| 94. Binary Tree Inorder Traversal | Cpp Python | Medium | 1. DFS recursion 2. explicit stack |
| 118. Pascal's Triangle | Python | Easy | iter/recur |
| 119. Pascal's Triangle II | Python | Easy | iter/recur |
| 130. Surrounded Regions | Python | Medium | BFS-2dimension |
| 133. Clone Graph | Cpp Python | Medium | 1. DFS, visited hashmap 2. BFS: add all neighbors to queue and traverse |
| 137. Single Number II | Python | Medium | bitwise |
| 138. Copy List with Random Pointer | Python | Medium | 1.backtracing 2.continuous copied node in space |
| 150. Evaluate Reverse Polish Notation | Python | Medium | stack |
| 153. Find Minimum in Rotated Sorted Array | Python | Medium | binary search |
| 155. Min Stack | Cpp | Easy | 1. two stack to store data and minimum 2. pair<data, minimum>, and var min to store current minimum. |
| 168. Excel Sheet Column Title | Python | Easy | DFS iteration |
| 171. Excel Sheet Column Number | Python | Easy | iteration 26-binary form |
| 179. Largest Number | Python | Medium | sort through splicing two number as string |
| 198. House Robber | Python | Medium | DP through the first two results of optimal solution |
| 200. Number of Islands | Cpp Python | Medium | 1. DFS: search to the depth of one element 2. BFS: search all neighbors of one element |
| 204. Count Primes | Python | Easy | set multiple of prime as composite number through prime list |
| 208. Implement Trie (Prefix Tree) ⭐ | Python | Medium | root trie recursive |
| 213. House Robber II | Python | Medium | divide two part to get local solution through DP |
| 218. The Skyline Problem | Python | Hard | scan + priority-queue |
| 220. Contains Duplicate III | Python | Medium | 1. bisection |
| 225. Implement Stack using Queues | Python | Easy | two queue operation to implement stack when pushing elements |
| 231. Power of Two | Python | Easy | bitwise, n as divisor |
| 232. Implement Queue using Stacks | Python | Easy | twice stack operation to implement queue |
| 263. Ugly Number | Python | Easy | factorization through 2,3,5 |
| 264. Ugly Number II | Python | Medium | minimum heap |
| 274. H-Index | Python | Medium | 1. Dichotomy 2. Counter array |
| 275. H-Index II | Python | Medium | 1. Dichotomy 2. traverse |
| 279. Perfect Squares | Cpp | Medium | BFS |
| 300. Longest Increasing Subsequence | Python | Medium | DP |
| 307. Range Sum Query - Mutable | Python | Medium | Segment Tree |
| 342. Power of Four | Python | Easy | 1. sqrt+powerOf2 2. Bitwise |
| 344. Reverse String | Cpp/Python | Easy | 1. double pointer 2. iteration or recursion of swap in place |
| 345. Reverse Vowels of a String | Python | Medium | 1. recursive with cache 2. DP |
| 377. Combination Sum IV | Python | Medium | 1. recursive with cache 2. DP |
| 394. Decode String | Python | Medium | 1. assistant stack 2. DFS |
| 395. Longest Substring with At Least K Repeating Characters | Python | Medium | DC |
| 421. Maximum XOR of Two Numbers in an Array | Python | Medium | bitwise |
| 424. Longest Repeating Character Replacement | Python | Medium | slide window with two pointer - char number counter with list - r-l+1-window_maxn > k |
| 448. Find All Numbers Disappeared in an Array | Python | Easy | ~ |
| 451. Sort Characters By Frequency | Python | Medium | ordered dict |
| 461. Hamming Distance | Python | Easy | XOR+NumberOf1 |
| 477. Total Hamming Distance | Python | Medium | Bitwise |
| 485. Max Consecutive Ones | Python | Easy | traverse and find max_count: return max(max_count, count) |
| 494. Target Sum | Cpp | Medium | 1. DFS: enumerate all possibility |
| 509. Fibonacci Number | Python | Easy | recur+hashmap (memerization to reduce repeated calculation) |
| 561. Array Partition I | Python | Easy | sort and combine |
| 567. Permutation in String | Python | Medium | slide window |
| 576. Out of Boundary Paths | Python | Medium | 1. DFS with memorization 2. DP |
| 581. Shortest Unsorted Continuous Subarray | Python | Medium | 1. sort and compare 2. find the law |
| 633. Sum of Square Numbers | Python | Medium | 1. enumeration 2. double pointer |
| 643. Maximum Average Subarray I | Python | Easy | slide window, start pointer is outside of initial window |
| 645. Set Mismatch | Python | Easy | count-array |
| 665. Non-decreasing Array | Python | Easy | tranverse to find valley and judge index of i-1, i, i+1 |
| 692. Top K Frequent Words | Python | Medium | 1. hashtable+sort 2. priority queue |
| 697. Degree of an Array | Python | Easy | hashtable records [counts, left_one right_one] |
| 703. Kth Largest Element in a Stream | Python | Easy | python heapq in no need of sorted operation |
| 704. Binary Search♥ | Python | Easy | 1. two pointer 2. recursive |
| 726. Number of Atoms | Python | Hard | stack with hashtable |
| 739. Daily Temperatures | Python | Medium | Monotonic stack |
| 740. Delete and Earn | Python | Medium | DP(rob house) |
| 743. Network Delay Time | Python | Medium | Dijkstra |
| 752. Open the Lock♥ | Cpp | Medium | BFS: transform to graph to find the shortest path |
| 783. Minimum Distance Between BST Nodes | Python | Easy | in-order traverse |
| 832. Flipping an Image | Python | Easy | 1. double pointer to reverse list 2. ^ XOR |
| 872. Leaf-Similar Trees | Python | Easy | DFS yield |
| 888. Fair Candy Swap | Python | Easy | hash table |
| 896. Monotonic Array | Python | Easy | set inc and des flags |
| 897. Increasing Order Search Tree | Python | Easy | in_order traversal |
| 912. Sort an Array | Python | Medium | 1. quick sort |
| 930. Binary Subarrays With Sum | Python | Medium | 1. Prefix sum 2. slide window |
| 938. Range Sum of BST | Python | Easy | BFS, DFS |
| 978. Longest Turbulent Subarray | Python | Medium | 1. slide window 2. Dynamic Programming |
| 993. Cousins in Binary Tree | Python | Easy | BFS, DFS (nonlocal) |
| 1006. Clumsy Factorial | Python | Medium | 1. stack to expression calculator with operator |
| 1011. Capacity To Ship Packages Within D Days | Python | Medium | binary search with greedy thinking |
| 1035. Uncrossed Lines | Python | Medium | 2D-DP |
| 1052. Grumpy Bookstore Owner | Python | Medium | 1. slide window 生气的老板 |
| 1143. Longest Common Subsequence | Python | Medium | 1. 2D-DP |
| 1190. Reverse Substrings Between Each Pair of Parentheses | Python | Medium | 1. stack/recursive |
| 1310. XOR Queries of a Subarray | Python | Medium | XOR, prefix sum |
| 1337. The K Weakest Rows in a Matrix | Python | Easy | Dichotomy+Mini-Heap |
| 1418. Display Table of Food Orders in a Restaurant | Python | Medium | Hashtable |
| 1423. Maximum Points You Can Obtain from Cards | Python | Medium | slide window + reverse thinking |
| 1438. Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit | Python | Medium | slide window + sortedlist(sortedcontainer) |
| 1442. Count Triplets That Can Form Two Arrays of Equal XOR | Python | Medium | XOR, prefix sum, mapping |
| 1482. Minimum Number of Days to Make m Bouquets | Python | Medium | binary search with checkDay func |
| 1486. XOR Operation in an Array | Python | Easy | XOR |
| 1711. Count Good Meals | Python | Medium | hashtable, traverse targets |
| 1720. Decode XORed Array | Python | Easy | XOR |
| 1734. Decode XORed Permutation | Python | Medium | XOR |
| 1736. Latest Time by Replacing Hidden Digits | Python | Easy | Greedy, bitwise judgement |
| 1738. Find Kth Largest XOR Coordinate Value | Python | Medium | Prefix sum and sort |
| 1818. Minimum Absolute Sum Difference | Python | Medium | bisect |
| 1833. Maximum Ice Cream Bars | Python | Medium | sort+greedy |
| 1893. Check if All the Integers in a Range Are Covered | Python | Easy | diff array + prefix sum |
| ----- | -------- | :--------: | ---------- |
| LCP 07. 传递信息 | Python | Easy | DFS |
| 面试题 17.10. Find Majority Element LCCI | Python | Easy | Boyer-Moore vote algo to find mode |
133. Clone Graph
200. Number of Islands
94. Binary Tree Inorder Traversal
133. Clone Graph
200. Number of Islands
⭐394. Decode String
494. Target Sum
576. Out of Boundary Paths
872. Leaf-Similar Trees
938. Range Sum of BST
993. Cousins in Binary Tree
494. Target Sum
576. Out of Boundary Paths
930. Binary Subarrays With Sum
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