LeetCode

Up to date (2015-05-26), there are 202 Algorithms / 12 Database / 4 Shell problems on LeetCode Online Judge. The number of problems is increasing recently. Here is the classification of all 218 problems. For extra problems and solutions, you can see my LintCode repo. I'll keep updating for full summary and better solutions. Stay tuned for updates. (Notes: "📖" means you have to buy the book from LeetCode. )

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Algorithms

• Bit Manipulation
• Array
• String
• Linked List
• Stack
• Heap
• Tree
• Hash Table
• Data Structure
• Math
• Two Pointer
• Sort
• Brute Force Search
• Divide and Conquer
• Binary Search
• Breadth-First Search
• Depth-First Search
• Dynamic Programming
• Backtracking
• Greedy

Database

• SQL

Shell

• Shell Script

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##Bit Manipulation

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 136 | Single Number | Python | O(n) | O(1) | Medium || 137 | Single Number II | Python | O(n) | O(1) | Medium || 190 | Reverse Bits | Python | O(n) | O(1) | Easy || 191 |Number of 1 Bits | Python | O(m) | O(1) | Easy || 201 | Bitwise AND of Numbers Range | Python | O(1) | O(1) | Medium ||

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##Array

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 15 | 3 Sum | Python | O(n^2) | O(1) | Medium || 16 | 3 Sum Closest | Python| O(n^2) | O(1) | Medium || 26 | Remove Duplicates from Sorted Array| Python | O(n) | O(1) | Easy || 27 | Remove Element | Python | O(n) | O(1) | Easy || 31 | Next Permutation| Python | O(n) | O(1) | Medium || Tricky 41 | First Missing Positive| Python | O(n) | O(1) | Hard || Tricky 48 | Rotate Image | Python | O(n^2) | O(1) | Medium || 54 | Spiral Matrix | Python | O(m * n) | O(1) | Medium || 59 | Spiral Matrix II | Python | O(m * n) | O(1) | Medium || 66 | Plus One | Python | O(n) | O(1) | Easy || 73 | Set Matrix Zeroes | Python | O(m * n) | O(1) | Medium || 80 | Remove Duplicates from Sorted Array II| Python | O(n) | O(1) | Medium || 118 | Pascal's Triangle| Python | O(n^2) | O(n) | Easy || 119 | Pascal's Triangle II| Python | O(n^2) | O(n) | Easy || 121 | Best Time to Buy and Sell Stock| Python | O(n) | O(1) | Medium || 128 | Longest Consecutive Sequence| Python | O(n) | O(n) | Hard || Tricky 157 | Read N Characters Given Read4 | Python | O(n) | O(1) | Easy |📖| 158 | Read N Characters Given Read4 II - Call multiple times | Python | O(n) | O(1) | Hard |📖| 163 | Missing Ranges| Python | O(n) | O(1) | Medium | 📖 | 169 | Majority Element | Python | O(n) | O(1) | Easy | 189 | Rotate Array | Python | O(n) | O(1) | Easy || 209 | Minimum Size Subarray Sum | [Python] (./Python/minimum-size-subarray-sum.py) | O(n) | O(1) | Medium || 215 | Kth Largest Element in an Array | [C++] (./C++/kth-largest-element-in-an-array.cpp) [Python] (./Python/kth-largest-element-in-an-array.py)| O(n) | O(1) | Medium | EPI|

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##String

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 5| Longest Palindromic Substring | Python | O(n) | O(n) | Medium || Manacher's Algorithm 6| ZigZag Conversion | Python | O(n) | O(1) | Easy || 8| String to Integer (atoi) | Python | O(n) | O(1) | Easy || 14| Longest Common Prefix | Python | O(n1 + n2 + ...) | O(1) | Easy || 28| Implement strStr() | Python | O(n + m) | O(m) | Easy || KMP Algorithm 38| Count and Say | Python| O(n * 2^n) | O(2^n) | Easy || 43| Multiply Strings | Python | O(m * n) | O(m + n) | Medium || 58| Length of Last Word | Python | O(n) | O(1) | Easy || 67| Add Binary | Python | O(n) | O(1) | Easy || 68| Text Justification | Python | O(n) | O(1) | Hard || 125| Valid Palindrome | Python | O(n) | O(1) | Easy || 151| Reverse Words in a String | Python | O(n) | O(n) | Medium || 161| One Edit Distance | Python | O(m + n) | O(1) | Medium |📖| 165| Compare Version Numbers | Python | O(n) | O(1) | Easy || 186| Reverse Words in a String II | Python | O(n) | O(1) | Medium | 📖 | 205| Isomorphic Strings | Python | O(n) | O(1) | Easy ||
214| Shortest Palindrome | C++ Python | O(n) | O(n) | Hard || KMP Algorithm Manacher's Algorithm

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##Linked List

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 2| Add Two Numbers | Python | O(n) | O(1) | Medium || 24| Swap Nodes in Pairs| Python | O(n) | O(1) | Medium || 25| Reverse Nodes in k-Group| Python | O(n) | O(1) | Hard || 61| Rotate List| Python | O(n) | O(1) | Medium ||
82| Remove Duplicates from Sorted List II| Python | O(n) | O(1) | Medium || 83| Remove Duplicates from Sorted List| Python | O(n) | O(1) | Easy || 92| Reverse Linked List II| Python | O(n) | O(1) | Medium || 138| Copy List with Random Pointer | Python | O(n) | O(1) | Hard || 160| Intersection of Two Linked Lists| Python | O(m + n) | O(1) | Easy || 203| Remove Linked List Elements| Python | O(n) | O(1) | Easy || 206| Reverse Linked List| Python | O(n) | O(1) | Easy ||

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##Stack

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 20| Valid Parentheses| Python | O(n) | O(n) | Easy || 32| Longest Valid Parentheses| Python | O(n) | O(1) | Hard || 71| Simplify Path| Python | O(n) | O(n) | Medium || 101| Symmetric Tree| Python | O(n) | O(h) | Easy || 150| Evaluate Reverse Polish Notation| Python| O(n)| O(n)| Medium || 155| Min Stack | Python | O(n) | O(1) | Easy || 173| Binary Search Tree Iterator | Python | O(1)| O(h)| Medium ||

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##Heap

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 23| Merge k Sorted Lists | Python | O(nlogk)| O(k)| Hard ||

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##Tree

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 94 | Binary Tree Inorder Traversal | Python | O(n)| O(1)| Medium || Morris Traversal | 99 | Recover Binary Search Tree | Python | O(n)| O(1)| Hard || Morris Traversal 144 | Binary Tree Preorder Traversal | Python | O(n)| O(1)| Medium || Morris Traversal 145 | Binary Tree Postorder Traversal | Python | O(n)| O(1)| Hard || Morris Traversal 208 | Implement Trie (Prefix Tree) | Python | O(n) | O(1) | Medium || Trie 211 | Add and Search Word - Data structure design | C++ Python | O(min(n, h)) | O(min(n, h)) | Medium || Trie, DFS 212| Word Search II | C++ Python | O(m * n * l) | O(l) | Hard | LintCode | Trie, DFS

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##Hash Table

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 1| Two Sum | Python | O(n) | O(n) | Medium || 3| Longest Substring Without Repeating Characters | Python | O(n) | O(1) | Medium || 18| 4 Sum |Python | O(n^2 * p) | O(n^2 * p) | Medium || 30| Substring with Concatenation of All Words | Python | O(m * n * k) | O(n * k) | Hard || 36| Valid Sudoku | Python | O(n^2) | O(n) | Easy || 49| Anagrams | Python | O(n) | O(n) | Medium || 76| Minimum Window Substring | Python | O(n) | O(k) | Hard || 149| Max Points on a Line | Python | O(n^2) | O(n) | Hard || 159| Longest Substring with At Most Two Distinct Characters| Python | O(n^2) | O(1) | Hard |📖| 170| Two Sum III - Data structure design | Python | O(n) | O(n) | Easy | 📖 | 187| Repeated DNA Sequences | Python | O(n) | O(n) | Medium || 202| Happy Number | Python | O(k) | O(k) | Easy || 204| Count Primes | Python | O(n) | O(n) | Easy || 217| Contains Duplicate | C++ Python | O(n) | O(n) | Easy ||

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##Data Structure

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 146| LRU Cache | Python | O(1) | O(n) | Hard ||

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##Math

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 7| Reverse Integer | Python | O(logn) | O(1) | Easy || 9| Palindrome Number | Python | O(1) | O(1) | Easy || 12| Integer to Roman | Python | O(n) | O(1) | Medium || 13| Roman to Integer | Python | O(n) | O(1) | Easy || 29| Divide Two Integers | Python | O(logn) | O(1) | Medium || 60| Permutation Sequence | Python | O(n^2) | O(n) | Medium || Cantor Ordering 65| Valid Number | Python | O(n) | O(1) | Hard || Automata 89| Gray Code | Python | O(2^n) | O(1) | Medium || 166| Fraction to Recurring Decimal | Python | O(logn) | O(1) | Medium || 168| Excel Sheet Column Title | Python | O(logn) | O(1) | Easy || 171| Excel Sheet Column Number | Python | O(n) | O(1) | Easy || 172| Factorial Trailing Zeroes | Python | O(logn) | O(1) | Easy ||

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##Sort

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 21| Merge Two Sorted Lists| Python | O(n) | O(1) | Easy || 56| Merge Intervals| Python | O(nlogn) | O(1) | Hard || 57| Insert Interval| Python | O(n) | O(1) | Hard || 75| Sort Colors | Python | O(n) | O(1) | Medium || 88| Merge Sorted Array| Python | O(n) | O(1) | Easy || 147| Insertion Sort List|Python | O(n^2) | O(1) | Medium || 148| Sort List | Python | O(nlogn) | O(logn) | Medium || 164| Maximum Gap | Python| O(n) | O(n) | Hard || Tricky 179| Largest Number | Python | O(nlogn) | O(1) | Medium || 218| The Skyline Problem | C++ | O(nlogn) | O(n) | Hard ||

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##Two Pointer

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 19| Remove Nth Node From End of List| Python | O(n) | O(1) | Easy || 86| Partition List| Python | O(n) | O(1) | Medium || 141| Linked List Cycle| Python | O(n) | O(1) | Medium || 142| Linked List Cycle II| Python | O(n) | O(1) | Medium || 143| Reorder List| Python | O(n) | O(1) | Medium ||
167| Two Sum II - Input array is sorted | Python | O(n) | O(1) | Medium | 📖 |

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##Brute Force Search

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 17| Letter Combinations of a Phone Number| Python | O(n * 4^n) | O(n) | Medium || 46| Permutations| Python | O(n!) | O(n) | Medium || 47| Permutations II| Python | O(n!) | O(n) | Hard || 78| Subsets | Python | O(n * 2^n) | O(1) | Medium || 90| Subsets II | Python | O(n * 2^n) | O(1) | Medium ||

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##Divide and Conquer

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 95| Unique Binary Search Trees II | Python | O(4^n / n^(3/2) | O(4^n / n^(3/2) | Medium || 98| Validate Binary Search Tree|Python| O(n) | O(1) | Medium || 100| Same Tree |Python | O(n) | O(h) | Easy || 104| Maximum Depth of Binary Tree|Python| O(n) | O(h) | Easy || 105| Construct Binary Tree from Preorder and Inorder Traversal | Python | O(n) | O(n) | Medium || 106| Construct Binary Tree from Inorder and Postorder Traversal | Python | O(n) | O(n) | Medium || 108| Convert Sorted Array to Binary Search Tree | Python | O(n) | O(logn) | Medium || 109| Convert Sorted List to Binary Search Tree | Python | O(n) | O(logn) | Medium || 110| Balanced Binary Tree | Python | O(n)| O(h) | Easy || 111| Minimum Depth of Binary Tree|Python| O(n) | O(h) | Easy || 114| Flatten Binary Tree to Linked List|Python| O(n) | O(h) | Medium || 116| Populating Next Right Pointers in Each Node|Python| O(n) | O(1) | Medium || 124| Binary Tree Maximum Path Sum| Python | O(n)| O(h)| Hard ||
129| Sum Root to Leaf Numbers | Python | O(n) | O(h) | Medium || 156| Binary Tree Upside Down | Python | O(n) | O(1) | Medium |📖|

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##Binary Search

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 4| Median of Two Sorted Arrays | Python | O(log(m + n)) | O(1) | Hard || 33| Search in Rotated Sorted Array | Python | O(logn) | O(1) | Hard || 34| Search for a Range | Python | O(logn) | O(1) | Medium || 35| Search Insert Position | Python | O(logn) | O(1) | Medium || 50| Pow(x, n) | Python | O(logn) | O(logn) | Medium || 69| Sqrt(x) | Python | O(logn) | O(1) | Medium || 74| Search a 2D Matrix | Python | O(logm + logn) | O(1) | Medium || 81| Search in Rotated Sorted Array II | Python | O(logn) | O(1) | Medium || 153| Find Minimum in Rotated Sorted Array | Python | O(logn) | O(1) | Medium || 154| Find Minimum in Rotated Sorted Array II | Python | O(logn) ~ O(n) | O(1) | Hard || 162| Find Peak Element | Python | O(logn) | O(1) | Medium ||

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##Breadth-First Search

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 102| Binary Tree Level Order Traversal| Python| O(n)| O(n)| Easy || 107| Binary Tree Level Order Traversal II| Python | O(n)| O(n)| Easy || 103| Binary Tree Zigzag Level Order Traversal| Python | O(n)| O(n)| Medium ||
117| Populating Next Right Pointers in Each Node II|Python| O(n) | O(1) | Hard || 127| Word Ladder|Python | O(n * d) | O(d) | Medium || 130| Surrounded Regions|Python| O(m * n) | O(m + n) | Medium || 133| Clone Graph| Python | O(n) | O(n) | Medium || 207| Course Schedule| Python | O(|V| + |E|) | O(|E|) | Medium || 210| Course Schedule II| Python | O(|V| + |E|) | O(|E|) | Medium ||

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##Depth-First Search

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 22| Generate Parentheses| Python| O(4^n / n^(3/2)) | O(n) | Medium || 37| Sudoku Solver | Python | O((9!)^9) | O(1) | Hard || 39| Combination Sum| Python | O(n^m) | O(m) | Medium || 40| Combination Sum II| Python| O(n! / m!(n-m)!)| O(m) | Medium || 51| N-Queens | Python | O(n!) | O(n) | Hard || 52| N-Queens-II | Python | O(n!) | O(n) | Hard || 77| Combinations | Python | O(n!) | O(n) | Medium || 79| Word Search | Python | O(m * n * l) | O(l) | Medium || 93| Restore IP Addresses | Python | O(n^m) ~ O(3^4) | O(n * m) ~ O(3 * 4) | Medium || 112| Path Sum | Python | O(n) | O(h) | Easy || 113| Path Sum II | Python | O(n) | O(h) | Medium || 131| Palindrome Partitioning | Python | O(n^2) ~ O(2^n) | O(n^2) | Medium || 199| Binary Tree Right Side View | Python | O(n) | O(h) | Medium || 200| Number of Islands | Python | O(m * n) | O(m * n)| Medium || 216| Combination Sum III| C++ Python | O(C(n, k)) | O(k) | Medium ||

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##Dynamic Programming

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 10| Regular Expression Matching | Python | O(m * n) | O(n) | Hard || 53| Maximum Subarray|Python| O(n) | O(1) | Medium || 62| Unique Paths | Python| O(m * n) | O(m + n) | Medium || 63| Unique Paths II | Python | O(m * n) | O(m + n) | Medium || 64| Minimum Path Sum|Python| O(m * n) | O(m + n) | Medium || 70| Climbing Stairs| Python | O(n) | O(1) | Easy || 72| Edit Distance|Python| O(m * n) | O(m + n) | Hard || 85| Maximal Rectangle|Python| O(n^2) | O(n) | Hard || 87| Scramble String | Python | O(n^4) | O(n^3) | Hard || 91| Decode Ways | Python| O(n) | O(1) | Medium || 96| Unique Binary Search Trees | Python | O(n^2) | O(n) | Medium || 97| Interleaving String|Python| O(m * n) | O(m + n) | Hard || 115| Distinct Subsequences|Python| O(n^2) | O(n) | Hard || 120| Triangle | Python | O(m * n) | O(n) | Medium || 123| Best Time to Buy and Sell Stock III | Python | O(n) | O(1) | Hard || 132| Palindrome Partitioning II | Python | O(n^2) | O(n^2) | Hard || 139| Word Break | Python | O(n^2) | O(n) | Medium || 140| Word Break II | Python | O(n^2) | O(n) | Hard || 152| Maximum Product Subarray|Python| O(n) | O(1) | Medium || 174| Dungeon Game | Python| O(m * n) | O(m + n) | Hard || 188| Best Time to Buy and Sell Stock IV| Python | O(k * n) | O(k) | Hard || 198| House Robber| Python | O(n) | O(1) | Easy || 213| House Robber II| C++ Python | O(n) | O(1) | Medium ||

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##Backtracking

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 126| Word Ladder II |Python | O(n * d) | O(d) | Hard ||

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##Greedy

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 11| Container With Most Water| Python | O(n) | O(1) | Medium || 42| Trapping Rain Water | Python | O(n) | O(1) | Hard || Tricky 44| Wildcard Matching | Python | O(m + n) | O(1) | Hard || Tricky 45| Jump Game II | Python | O(n) | O(1) | Hard || 55| Jump Game | Python | O(n) | O(1) | Medium || 84| Largest Rectangle in Histogram | Python | O(n) | O(n) | Hard || Tricky 122| Best Time to Buy and Sell Stock II| Python | O(n) | O(1) | Medium || 134| Gas Station| Python | O(n) | O(1) | Medium || 135| Candy| Python | O(n) | O(n) | Hard ||

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##SQL

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 175| Combine Two Tables | MySQL | O(m + n) | O(m + n) | Easy || 176| Second Highest Salary | MySQL | O(n) | O(1) | Easy || 177| Nth Highest Salary | MySQL | O(n^2) | O(n) | Medium || 178| Rank Scores | MySQL | O(n^2) | O(n) | Medium || 180| Consecutive Numbers | MySQL | O(n) | O(n) | Medium || 181| Employees Earning More Than Their Managers | MySQL | O(n^2) | O(1) | Easy || 182| Duplicate Emails | MySQL | O(n^2) | O(n) | Easy || 183| Customers Who Never Order | MySQL | O(n^2) | O(1) | Easy || 184| Department Highest Salary | MySQL | O(n^2) | O(n) | Medium || 185| Department Top Three Salaries | MySQL | O(n^2) | O(n) | Hard || 196| Delete Duplicate Emails | MySQL | O(n^2) | O(n) | Easy || 197| Rising Temperature | MySQL | O(n^2) | O(n) | Easy ||

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##Shell Script

| Problem | Solution | Time | Space | Difficulty | Tag | Notes

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 192 | Word Frequency | Shell | O(n) | O(k) | Medium || 193 | Valid Phone Numbers | Shell | O(n) | O(1) | Easy || 194 | Transpose File | Shell | O(n^2) | O(n^2) | Medium || 195 | Tenth Line | Shell | O(n) | O(1) | Easy ||