Up to date (2016-12-18), there are 447 Algorithms / 13 Database / 4 Shell / 4 Draft questions on LeetCode Online Judge. The number of questions is increasing recently. Here is the classification of all 468 questions. For more questions and solutions, you can see my LintCode repository. I'll keep updating for full summary and better solutions. Stay tuned for updates. (Notes: "📖" means you need to subscribe to LeetCode premium membership for the access to premium questions.)

• Bit Manipulation
• Array
• String
• Linked List
• Stack
• Queue
• Heap
• Tree
• Hash Table
• Data Structure
• Math
• Two Pointers
• Sort
• Recursion
• Binary Search
• Binary Search Tree
• Breadth-First Search
• Depth-First Search
• Backtracking
• Dynamic Programming
• Greedy
• Design

• SQL

• Shell Script

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 136 | Single Number | C++ Python | O(n) | O(1) | Easy || 137 | Single Number II | C++ Python | O(n) | O(1) | Medium || 190 | Reverse Bits | C++ Python | O(1) | O(1) | Easy || 191 |Number of 1 Bits | C++ Python | O(1) | O(1) | Easy || 201 | Bitwise AND of Numbers Range | C++ Python | O(1) | O(1) | Medium || 231 | Power of Two | C++ Python | O(1) | O(1) | Easy | LintCode | 260 | Single Number III | C++ Python | O(n) | O(1) | Medium || 268| Missing Number | C++ Python | O(n) | O(1) | Medium | LintCode || 318| Maximum Product of Word Lengths | C++ Python | O(n) ~ O(n^2) | O(n) | Medium || Bit Manipulation, Counting Sort, Pruning| 342 | Power of Four | C++ Python | O(1) | O(1) | Easy | | 371 | Sum of Two Integers | C++ Python | O(1) | O(1) | Easy | LintCode | 389 | Find the Difference | C++ Python | O(n) | O(1) | Easy | | 393 | UTF-8 Validation | C++ Python | O(n) | O(1) | Medium | | 401 | Binary Watch | C++ Python | O(1) | O(1) | Easy | | 411 | Minimum Unique Word Abbreviation | C++ Python | O(2^n) | O(n) | Hard | 📖 | 421 | Maximum XOR of Two Numbers in an Array | C++ Python | O(n) | O(1) | Medium || 461 | Hamming Distance | C++ Python | O(1) | O(1) | Easy || 462 | Minimum Moves to Equal Array Elements II | C++ Python | O(n) on average | O(1) | Medium || 477 | Total Hamming Distance | C++ Python | O(n) | O(1) | Medium ||

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 15 | 3 Sum | C++ Python | O(n^2) | O(1) | Medium || Two Pointers 16 | 3 Sum Closest | C++ Python | O(n^2) | O(1) | Medium || Two Pointers 18| 4 Sum | C++ Python | O(n^3) | O(1) | Medium || Two Pointers 26 | Remove Duplicates from Sorted Array| C++ Python | O(n) | O(1) | Easy || Two Pointers 27 | Remove Element | C++ Python | O(n) | O(1) | Easy || 31 | Next Permutation| C++ Python | O(n) | O(1) | Medium || Tricky 41 | First Missing Positive| C++ Python | O(n) | O(1) | Hard || Tricky 48 | Rotate Image | C++ Python | O(n^2) | O(1) | Medium || 54 | Spiral Matrix | C++ Python | O(m * n) | O(1) | Medium || 59 | Spiral Matrix II | C++ Python | O(n^2) | O(1) | Medium || 66 | Plus One | C++ Python | O(n) | O(1) | Easy || 73 | Set Matrix Zeroes | C++ Python | O(m * n) | O(1) | Medium || 80 | Remove Duplicates from Sorted Array II| C++ Python | O(n) | O(1) | Medium || Two Pointers 118 | Pascal's Triangle| C++ Python | O(n^2) | O(1) | Easy || 119 | Pascal's Triangle II| C++ Python | O(n^2) | O(1) | Easy || 121 | Best Time to Buy and Sell Stock| C++ Python | O(n) | O(1) | Easy || 128 | Longest Consecutive Sequence| C++ Python | O(n) | O(n) | Hard || Tricky 157 | Read N Characters Given Read4 | C++ Python | O(n) | O(1) | Easy |📖| 158 | Read N Characters Given Read4 II - Call multiple times | C++ Python | O(n) | O(1) | Hard |📖| 163 | Missing Ranges| C++ Python | O(n) | O(1) | Medium | 📖 | 169 | Majority Element | C++ Python | O(n) | O(1) | Easy | 189 | Rotate Array | C++ Python | O(n) | O(1) | Easy || 209 | Minimum Size Subarray Sum | [C++] (./C++/minimum-size-subarray-sum.cpp) [Python] (./Python/minimum-size-subarray-sum.py) | O(n) | O(1) | Medium | | Binary Search 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(n^2) | O(1) | Medium | EPI| 228 | Summary Ranges | [C++] (./C++/summary-ranges.cpp) [Python] (./Python/summary-ranges.py)| O(n) | O(1) | Medium | | 229 | Majority Element II | C++ Python | O(n) | O(1) | Medium | | 238 | Product of Array Except Self | C++ Python | O(n) | O(1) | Medium | LintCode | 240 | Search a 2D Matrix II | C++ Python | O(m + n) | O(1) | Medium | EPI, LintCode | 243| Shortest Word Distance | C++ Python | O(n) | O(1) | Easy |📖|| 245| Shortest Word Distance III | C++ Python | O(n) | O(1) | Medium |📖|| 251| Flatten 2D Vector | C++ Python | O(1) | O(1) | Medium |📖|| 277| Find the Celebrity | C++ Python | O(n) | O(1) | Medium |📖, EPI || 289| Game of Life | C++ Python | O(m * n) | O(1) | Medium ||| 293| Flip Game | C++ Python | O(n * (c+1)) | O(1) | Easy |📖|| 296| Best Meeting Point | C++ Python | O(m * n) | O(m + n) | Hard |📖|| 311| Sparse Matrix Multiplication | C++ Python | O(m * n * l) | O(m * l) | Medium |📖|| 334| Increasing Triplet Subsequence | C++ Python | O(n) | O(1) | Medium ||| 370| Range Addition | C++ Python | O(k + n) | O(1) | Medium |📖|| 384| Shuffle an Array | C++ Python | O(n) | O(n) | Medium | EPI || 396| Rotate Function | C++ Python | O(n) | O(1) | Easy ||| 412| Fizz Buzz | C++ Python | O(n) | O(1) | Easy ||| 414| Third Maximum Number | C++ Python | O(n) | O(1) | Easy ||| 419| Battleships in a Board | C++ Python | O(m * n) | O(1) | Medium ||| 422| Valid Word Square | C++ Python | O(m * n) | O(1) | Easy |📖|| 442| Find All Duplicates in an Array | C++ Python | O(n) | O(1) | Medium ||| 448| Find All Numbers Disappeared in an Array | C++ Python | O(n) | O(1) | Easy |||

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 5| Longest Palindromic Substring | C++ Python | O(n) | O(n) | Medium || Manacher's Algorithm 6| ZigZag Conversion | C++ Python | O(n) | O(1) | Easy || 8| String to Integer (atoi) | C++ Python | O(n) | O(1) | Easy || 14| Longest Common Prefix | C++ Python | O(n * k) | O(1) | Easy || 28| Implement strStr() | C++ Python | O(n + k) | O(k) | Easy || KMP Algorithm 38| Count and Say | C++ Python| O(n * 2^n) | O(2^n) | Easy || 43| Multiply Strings | C++ Python | O(m * n) | O(m + n) | Medium || 58| Length of Last Word | C++ Python | O(n) | O(1) | Easy || 67| Add Binary | C++ Python | O(n) | O(1) | Easy || 68| Text Justification | C++ Python | O(n) | O(1) | Hard || 125| Valid Palindrome | C++ Python | O(n) | O(1) | Easy || 151| Reverse Words in a String | C++ Python | O(n) | O(1) | Medium || 161| One Edit Distance | C++ Python | O(m + n) | O(1) | Medium |📖 | 165| Compare Version Numbers | C++ Python | O(n) | O(1) | Easy || 186| Reverse Words in a String II |C++ Python | O(n) | O(1) | Medium | 📖 | 214| Shortest Palindrome | C++ Python | O(n) | O(n) | Hard || KMP Algorithm Manacher's Algorithm 242| Valid Anagram| C++ Python | O(n) | O(1) | Easy | LintCode | 271| Encode and Decode Strings | C++ Python | O(n) | O(1) | Medium | 📖 | 273| Integer to English Words | C++ Python | O(logn) | O(1) | Hard | | 306| Addictive Number | C++ Python | O(n^3) | O(n) | Medium | | 383| Ransom Note | C++ Python | O(n) | O(1) | Easy | EPI | 405| Convert a Number to Hexadecimal | C++ Python | O(n) | O(1) | Easy | | 408| Valid Word Abbreviation | C++ Python | O(n) | O(1) | Easy | 📖 | 415| Add Strings | C++ Python | O(n) | O(1) | Easy | | 420| Strong Password Checker | C++ Python | O(n) | O(1) | Hard | | 434| Number of Segments in a String | C++ Python | O(n) | O(1) | Easy | | 459| Repeated Substring Pattern | C++ Python | O(n) | O(n) | Easy || KMP Algorithm | 468| Validate IP Address | C++ Python | O(1) | O(1) | Medium | |

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 2| Add Two Numbers | C++ Python | O(n) | O(1) | Medium || 21| Merge Two Sorted Lists| C++ Python | O(n) | O(1) | Easy || 23| Merge k Sorted Lists | C++ Python | O(nlogk)| O(1)| Hard | | Heap, Divide and Conquer 24| Swap Nodes in Pairs| C++ Python | O(n) | O(1) | Easy || 25| Reverse Nodes in k-Group| C++ Python | O(n) | O(1) | Hard || 61| Rotate List| C++ Python | O(n) | O(1) | Medium ||
82| Remove Duplicates from Sorted List II| C++ Python | O(n) | O(1) | Medium || 83| Remove Duplicates from Sorted List| C++ Python | O(n) | O(1) | Easy || 92| Reverse Linked List II| C++ Python | O(n) | O(1) | Medium || 138| Copy List with Random Pointer | C++ Python | O(n) | O(1) | Hard || 160| Intersection of Two Linked Lists| C++ Python | O(m + n) | O(1) | Easy || 203| Remove Linked List Elements| C++ Python | O(n) | O(1) | Easy || 206| Reverse Linked List| C++ Python | O(n) | O(1) | Easy || 234| Palindrome Linked List| C++ Python | O(n) | O(1) | Easy || 237| Delete Node in a Linked List| C++ Python | O(1) | O(1) | Easy | LintCode | 328| Odd Even Linked List| C++ Python | O(n) | O(1) | Medium | | 369| Plus One Linked List| C++ Python | O(n) | O(1) | Medium | 📖 | Two Pointers | 445| Add Two Numbers II| C++ Python | O(m + n) | O(m + n) | Medium |||

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 20| Valid Parentheses| C++ Python | O(n) | O(n) | Easy || 32| Longest Valid Parentheses| C++ Python | O(n) | O(1) | Hard || 71| Simplify Path| C++ Python | O(n) | O(n) | Medium || 84| Largest Rectangle in Histogram | C++ Python | O(n) | O(n) | Hard || Ascending Stack, DP 85| Maximal Rectangle| C++ Python| O(m * n) | O(n) | Hard | EPI | Ascending Stack 101| Symmetric Tree| C++ Python | O(n) | O(h) | Easy || 150| Evaluate Reverse Polish Notation| C++ Python| O(n)| O(n)| Medium || 155| Min Stack | C++ Python | O(n) | O(1) | Easy || 173| Binary Search Tree Iterator | C++ Python | O(1)| O(h)| Medium ||
224| Basic Calculator | C++ Python | O(n)| O(n)| Hard || 227| Basic Calculator II | C++ Python | O(n)| O(n)| Medium || 232| Implement Queue using Stacks | C++ Python | O(1), amortized| O(n)| Easy | EPI, LintCode | 255| Verify Preorder Sequence in Binary Search Tree | C++ Python | O(n)| O(1)| Medium |📖|| 272| Closest Binary Search Tree Value II | C++ Python | O(h + k)| O(h)| Hard |📖|| 331| Verify Preorder Serialization of a Binary Tree | C++ Python | O(n)| O(1)| Medium ||| 341| Flatten Nested List Iterator| C++ Python | O(n) | O(h) | Medium |📖| Iterator | 385| Mini Parser| C++ Python | O(n) | O(h) | Medium ||| 394| Decode String| C++ Python | O(n) | O(h) | Medium ||| 439| Ternary Expression Parser | C++ Python | O(n) | O(1) | Medium |📖| 456| 132 Pattern | C++ Python | O(n) | O(n) | Medium ||

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 239| Sliding Window Maximum| C++ Python | O(n) | O(k) | Hard | EPI, LintCode | 281| Zigzag Iterator| C++ Python | O(n) | O(k) | Medium |📖|| 346| Moving Average from Data Stream| C++ Python | O(1) | O(w) | Easy |📖||

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 264| Ugly Number II | C++ Python | O(n) | O(1) | Medium | CTCI, LintCode | BST, Heap | 295| Find Median from Data Stream | C++ Python | O(nlogn) | O(n) | Hard | EPI, LintCode | BST, Heap | 313| Super Ugly Number | C++ Python | O(n * k) | O(n + k) | Medium || BST, Heap | 358| Rearrange String k Distance Apart| C++ Python | O(n) | O(n) | Hard |📖| Greedy, Heap | 373 | Find K Pairs with Smallest Sums | C++ Python | O(k * log(min(n, m, k))) | O(min(n, m, k)) | Medium ||| 378 | Kth Smallest Element in a Sorted Matrix | C++ Python | O(k * log(min(n, m, k))) | O(min(n, m, k)) | Medium | LintCode || 407 | Trapping Rain Water II | C++ Python | O(m * n * (logm + logn)) | O(m * n) | Hard | LintCode ||

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 94 | Binary Tree Inorder Traversal | C++ Python | O(n)| O(1)| Medium || Morris Traversal | 99 | Recover Binary Search Tree | C++ Python | O(n)| O(1)| Hard || Morris Traversal 144 | Binary Tree Preorder Traversal | C++ Python | O(n)| O(1)| Medium || Morris Traversal 145 | Binary Tree Postorder Traversal | C++ Python | O(n)| O(1)| Hard || Morris Traversal 208 | Implement Trie (Prefix Tree) | C++ 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 226| Invert Binary Tree | C++ Python | O(n) | O(h), O(w) | Easy || 297 | Serialize and Deserialize Binary Tree | C++ Python | O(n) | O(h) | Hard | LintCode | DFS 307 | Range Sum Query - Mutable | C++ Python | ctor: O(n), update: O(logn), query: O(logn) | O(n) | Medium | LintCode | DFS, Segment Tree, BIT 308 | Range Sum Query 2D - Mutable | C++ Python | ctor: O(m * n), update: O(logm + logn), query: O(logm + logn) | O(m * n) | Hard | 📖 | DFS, Segment Tree, BIT 315|Count of Smaller Numbers After Self| C++ Python| O(nlogn) | O(n) | Hard | LintCode | BST, BIT, Divide and Conquer |

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 1| Two Sum | C++ Python | O(n) | O(n) | Easy || 3| Longest Substring Without Repeating Characters | C++ Python | O(n) | O(1) | Medium || 30| Substring with Concatenation of All Words | C++ Python | O(m * n * k) | O(n * k) | Hard || 36| Valid Sudoku | C++ Python | O(9^2) | O(9) | Easy || 49| Group Anagrams | C++ Python | O(n * glogg) | O(n) | Medium || 76| Minimum Window Substring | C++ Python | O(n) | O(k) | Hard || 149| Max Points on a Line | C++ Python | O(n^2) | O(n) | Hard || 159| Longest Substring with At Most Two Distinct Characters| C++ Python | O(n) | O(1) | Hard |📖| 170| Two Sum III - Data structure design | C++ Python | O(n) | O(n) | Easy | 📖 | 187| Repeated DNA Sequences | Python | O(n) | O(n) | Medium || 202| Happy Number | C++ Python | O(k) | O(k) | Easy || 204| Count Primes | C++ Python | O(n) | O(n) | Easy || 205| Isomorphic Strings | C++ Python | O(n) | O(1) | Easy || 217| Contains Duplicate | C++ Python | O(n) | O(n) | Easy || 219| Contains Duplicate II | C++ Python | O(n) | O(n) | Easy || 244| Shortest Word Distance II | C++ Python | ctor: O(n), lookup: O(a + b) | O(n) | Medium |📖|| 246| Strobogrammatic Number | C++ Python | O(n) | O(1) | Easy |📖|| 249| Group Shifted Strings | C++ Python | O(nlogn) | O(n) | Easy |📖|| 266| Palindrome Permutation | C++ Python | O(n) | O(1) | Easy |📖|| 288| Unique Word Abbreviation | C++ Python | ctor: O(n), lookup: O(1) | O(k) | Easy |📖|| 290| Word Pattern | C++ Python | O(n) | O(c) | Easy | variant of Isomorphic Strings || 299| Bulls and Cows | C++ Python | O(n) | O(1) | Easy ||| 305| Number of Islands II | C++ Python | O(k) | O(k)| Hard | LintCode, 📖 | Union Find 314| Binary Tree Vertical Order Traversal | C++ Python | O(n) | O(n)| Medium | 📖 | BFS 323| Number of Connected Components in an Undirected Graph | C++ Python | O(n) | O(n)| Medium | 📖 | Union Find 325| Maximum Size Subarray Sum Equals k | C++ Python | O(n) | O(n)| Medium | 📖 | 336| Palindrome Pairs | C++ Python | O(n * k^2) | O(n * k) | Hard | | | 340| Longest Substring with At Most K Distinct Characters| C++ Python | O(n) | O(1) | Hard |📖| 356| Line Reflection | C++ Python | O(n)| O(n)| Medium |📖| Hash, Two Pointers | 387| First Unique Character in a String | C++ Python | O(n)| O(n)| Easy ||| 388| Longest Absolute File Path | C++ Python | O(n)| O(d)| Medium || Stack | 409| Longest Palindrome | C++ Python | O(n)| O(1)| Easy ||| 424| Longest Repeating Character Replacement | C++ Python | O(n)| O(1)| Medium ||| 438| Find All Anagrams in a String | C++ Python | O(n) | O(1) | Easy || 447| Number of Boomerangs | C++ Python | O(n^2) | O(n) | Easy || 454| 4Sum II | C++ Python | O(n^2) | O(n^2) | Medium || 473| Matchsticks to Square | C++ Python | O(n * s * 2^n) | O(n * (2^n + s)) | Medium ||

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 146| LRU Cache | C++ Python | O(1) | O(k) | Hard || 225| Implement Stack using Queues | C++ Python | push: O(n), pop: O(1), top: O(1) | O(n) | Easy ||

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 7| Reverse Integer | C++ Python | O(1) | O(1) | Easy || 9| Palindrome Number | C++ Python | O(1) | O(1) | Easy || 12| Integer to Roman | C++ Python | O(n) | O(1) | Medium || 13| Roman to Integer | C++ Python | O(n) | O(1) | Easy || 29| Divide Two Integers | C++ Python | O(1) | O(1) | Medium || 50| Pow(x, n) | C++ Python | O(1) | O(1) | Medium || 60| Permutation Sequence | C++ Python | O(n^2) | O(n) | Medium || Cantor Ordering 65| Valid Number | C++ Python | O(n) | O(1) | Hard || Automata 89| Gray Code | C++ Python | O(2^n) | O(1) | Medium || 166| Fraction to Recurring Decimal | C++ Python | O(logn) | O(1) | Medium || 168| Excel Sheet Column Title | C++ Python | O(logn) | O(1) | Easy || 171| Excel Sheet Column Number | C++ Python | O(n) | O(1) | Easy || 172| Factorial Trailing Zeroes | C++ Python | O(1) | O(1) | Easy || 223| Rectangle Area | C++ Python | O(1) | O(1) | Easy || 233| Number of Digit One | C++ Python | O(1) | O(1) | Hard | CTCI, LintCode| 248| Strobogrammatic Number III | C++ Python | O(5^(n/2)) | O(n) | Hard |📖|| 258| Add Digits | C++ Python | O(1) | O(1) | Easy ||| 263| Ugly Number | C++ Python | O(1) | O(1) | Easy ||| 292| Nim Game | C++ Python | O(1) | O(1) | Easy | LintCode || 319 | Bulb Switcher | C++ Python | O(1) | O(1) | Medium ||| 326 | Power of Three | C++ Python | O(1) | O(1) | Easy ||| 335 | Self Crossing | C++ Python | O(n) | O(1) | Hard ||| 338 | Counting Bits | C++ Python | O(n) | O(n) | Medium ||| 343 | Integer Break | C++ Python | O(logn) | O(1) | Medium || Tricky, DP | 365 | Water and Jug Problem | C++ Python | O(logn) | O(1) | Medium || Euclidean Algorithm | 372 | Super Pow | C++ Python | O(n) | O(1) | Medium ||| 382 | Linked List Random Node | C++ Python | O(n) | O(1) | Medium || Reservoir Sampling | 386 | Lexicographical Numbers | C++ Python | O(n) | O(1) | Medium ||| 390 | Elimination Game | C++ Python | O(logn) | O(1) | Medium || 391 | Perfect Rectangle | C++ Python | O(n) | O(n) | Hard | | 398 | Random Pick Index | C++ Python | O(n) | O(1) | Medium || Reservoir Sampling | 400 | Nth Digit | C++ Python | O(logn) | O(1) | Easy ||| 413 | Arithmetic Slices | C++ Python | O(n) | O(1) | Medium ||| 423 | Reconstruct Original Digits from English | C++ Python | O(n) | O(1) | Medium | GCJ2016 - Round 1B|| 441 | Arranging Coins | C++ Python | O(nlogn) | O(1) | Easy || Binary Search| 453 | Minimum Moves to Equal Array Elements | C++ Python | O(n) | O(1) | Easy ||| 458 | Poor Pigs | C++ Python | O(n) | O(1) | Easy ||| 469 | Convex Polygon | C++ Python | O(n) | O(1) | Medium |📖||

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 56| Merge Intervals| C++ Python | O(nlogn) | O(1) | Hard || 57| Insert Interval| C++ Python | O(n) | O(1) | Hard || 75| Sort Colors | C++ Python | O(n) | O(1) | Medium || Tri Partition 88| Merge Sorted Array| C++ Python | O(n) | O(1) | Easy || 147| Insertion Sort List|C++ Python | O(n^2) | O(1) | Medium || 148| Sort List | C++ Python | O(nlogn) | O(logn) | Medium || 164| Maximum Gap | C++ Python| O(n) | O(n) | Hard || Tricky 179| Largest Number | C++ Python | O(nlogn) | O(1) | Medium || 218| The Skyline Problem | C++ Python | O(nlogn) | O(n) | Hard || Sort, BST| 252| Meeting Rooms | C++ Python | O(nlogn) | O(n) | Easy |📖| | 253| Meeting Rooms II | C++ Python | O(nlogn) | O(n) | Medium |📖| | 274| H-Index | C++ Python | O(n) | O(n) | Medium || Counting Sort | 280| Wiggle Sort | C++ Python | O(n) | O(1) | Medium |📖| | 324| Wiggle Sort II | C++ Python | O(n) on average | O(1) | Medium | variant of Sort Colors | Tri Partition | 347| Top K Frequent Elements | C++ Python | O(n) on average | O(n) | Medium | | Quick Select, Heap | 406| Queue Reconstruction by Height | C++ Python | O(n * sqrt(n)) | O(n) | Medium | | | 451| Sort Characters By Frequency | C++ Python | O(n) | O(n) | Medium | | |

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 19| Remove Nth Node From End of List| C++ Python | O(n) | O(1) | Easy || 86| Partition List| C++ Python | O(n) | O(1) | Medium || 141| Linked List Cycle| C++ Python | O(n) | O(1) | Easy || 142| Linked List Cycle II| C++ Python | O(n) | O(1) | Medium || 143| Reorder List| C++ Python | O(n) | O(1) | Medium ||
167| Two Sum II - Input array is sorted | C++ Python | O(n) | O(1) | Medium | | 259 | 3Sum Smaller | C++ Python | O(n^2) | O(1) | Medium | 📖, LintCode | 283 | Move Zeroes | C++ Python | O(n) | O(1) | Easy | | 287| Find the Duplicate Number| C++ Python | O(n) | O(1) | Hard | | Binary Search, Two Pointers | 344| Reverse String | C++ Python | O(n) | O(1) | Easy | | 345| Reverse Vowels of a String | C++ Python | O(n) | O(1) | Easy | | 349| Intersection of Two Arrays | C++ Python | O(m + n) | O(min(m, n)) | Easy | EPI | Hash, Binary Search 350| Intersection of Two Arrays II | C++ Python | O(m + n) | O(1) | Easy | EPI | Hash, Binary Search 360| Sort Transformed Array | C++ Python | O(n) | O(1) | Medium |📖| 457| Circular Array Loop | C++ Python | O(n) | O(1) | Medium ||

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 95| Unique Binary Search Trees II | C++ Python | O(4^n / n^(3/2) | O(4^n / n^(3/2) | Medium || 98| Validate Binary Search Tree|C++ Python| O(n) | O(1) | Medium || 100| Same Tree |C+ Python | O(n) | O(h) | Easy || 104| Maximum Depth of Binary Tree| C++ Python| O(n) | O(h) | Easy || 105| Construct Binary Tree from Preorder and Inorder Traversal | C++ Python | O(n) | O(n) | Medium || 106| Construct Binary Tree from Inorder and Postorder Traversal | C++ Python | O(n) | O(n) | Medium || 108| Convert Sorted Array to Binary Search Tree | C++ Python | O(n) | O(logn) | Medium || 109| Convert Sorted List to Binary Search Tree | C++ 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 |📖| 241| Different Ways to Add Parentheses | C++ Python | O(n * 4^n / n^(3/2)) | O(n * 4^n / n^(3/2)) | Medium || 298 | Binary Tree Longest Consecutive Sequence | C++ Python | O(n) | O(h) | Medium |📖| 327| Count of Range Sum | C++ Python | O(nlogn) | O(n) | Hard || 333 | Largest BST Subtree | C++ Python | O(n) | O(h) | Medium |📖| 337| House Robber III | C++ Python | O(n) | O(h) | Medium || 395| Longest Substring with At Least K Repeating Characters | C++ Python | O(n) | O(1) | Medium || 404| Sum of Left Leaves | C++ Python | O(n) | O(h) | Easy || 437| Path Sum III | C++ Python | O(n^2) | O(h) | Easy ||

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 4| Median of Two Sorted Arrays | C++ Python | O(log(min(m, n))) | O(1) | Hard || 33| Search in Rotated Sorted Array | C++ Python | O(logn) | O(1) | Hard || 34| Search for a Range | C++ Python | O(logn) | O(1) | Medium || 35| Search Insert Position | C++ Python | O(logn) | O(1) | Medium || 69| Sqrt(x) | C++ Python | O(logn) | O(1) | Medium || 74| Search a 2D Matrix | C++ Python | O(logm + logn) | O(1) | Medium || 81| Search in Rotated Sorted Array II | C++ Python | O(logn) | O(1) | Medium || 153| Find Minimum in Rotated Sorted Array | C++ Python | O(logn) | O(1) | Medium || 154| Find Minimum in Rotated Sorted Array II | C++ Python | O(logn) ~ O(n) | O(1) | Hard || 162| Find Peak Element | C++ Python | O(logn) | O(1) | Medium || 222| Count Complete Tree Nodes | C++ Python | O((logn)^2) | O(1) | Medium || 275| H-Index II | C++ Python | O(logn) | O(1) | Medium || Binary Search | 278| First Bad Version | C++ Python | O(logn) | O(1) | Easy | LintCode || 300| Longest Increasing Subsequence | C++ Python | O(nlogn) | O(n) | Medium | CTCI, LintCode | Binary Search, DP| 302| Smallest Rectangle Enclosing Black Pixels| C++ Python | O(nlogn) | O(1) | Hard | 📖 | 354| Russian Doll Envelopes | C++ Python | O(nlogn) | O(1) | Hard ||| 363| Max Sum of Rectangle No Larger Than K | C++ Python | O(min(m, n)^2 * max(m, n) * logn(max(m, n))) | O(max(m, n)) | Hard ||| 367| Valid Perfect Square| C++ Python | O(logn) | O(1) | Medium | | 374| Guess Number Higher or Lower| C++ Python | O(logn) | O(1) | Easy | | 410| Split Array Largest Sum| C++ Python | O(nlogs) | O(1) | Hard | | 436 | Find Right Interval | C++ Python | O(nlogn) | O(n) | Medium | | 475 | Heaters | C++ Python | O((m + n) * logn) | O(1) | Easy | |

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 220| Contains Duplicate III | C++ Python | O(nlogk) | O(k) | Medium || 230 | Kth Smallest Element in a BST | C++ Python | O(max(h, k)) | O(min(h, k)) | Medium || 235 | Lowest Common Ancestor of a Binary Search Tree | C++ Python | O(h) | O(1) | Easy | EPI | 270| Closest Binary Search Tree Value| C++ Python | O(h) | O(1) | Easy | 📖 | 285| Inorder Successor in BST| C++ Python | O(h) | O(1) | Medium | 📖 | 352 | Data Stream as Disjoint Intervals | C++ Python | O(logn) | O(n) | Hard | | 449|Serialize and Deserialize BST| C++ Python| O(n) | O(h) | Medium | | | 450|Delete Node in a BST| C++ Python| O(h) | O(h) | Medium | | |

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 102| Binary Tree Level Order Traversal| C++ 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|C++ 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 || Topological Sort | 210| Course Schedule II| Python | O(|V| + |E|) | O(|E|) | Medium || Topological Sort | 261| Graph Valid Tree| C++ Python | O(|V| + |E|) | O(|V| + |E|) | Medium | 📖 | 269| Alien Dictionary | C++ Python | O(n) | O(1) | Hard |📖| Topological Sort, BFS, DFS | 286| Walls and Gates| C++ Python | O(m * n) | O(g) | Medium | 📖 | 310| Minimum Height Trees| C++ Python | O(n) | O(n) | Medium || 317| Shortest Distance from All Buildings| C++ Python | O(k * m * n) | O(m * n) | Hard | 📖 | 433| Minimum Genetic Mutation| C++ Python | O(n * b) | O(b) | Medium || 444| Sequence Reconstruction| C++ Python | O(n * s) | O(n) | Medium |📖| Topological Sort |

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 112| Path Sum | Python | O(n) | O(h) | Easy || 113| Path Sum II | Python | O(n) | O(h) | 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 || 236 | Lowest Common Ancestor of a Binary Tree | C++ Python | O(n) | O(h) | Medium | EPI | 247| Strobogrammatic Number II | C++ Python | O(n^2 * 5^(n/2)) | O(n) | Medium |📖|| 250| Count Univalue Subtrees | C++ Python | O(n) | O(h) | Medium |📖|| 257| Binary Tree Paths | C++ Python | O(n * h) | O(h) | Easy ||| 282| Expression Add Operators | C++ Python | O(4^n) | O(n) | Hard ||| 301| Remove Invalid Parentheses | C++ Python | O(C(n, c)) | O(c) | Hard ||| 329| Longest Increasing Path in a Matrix | C++ Python | O(m * n) | O(m * n) | Hard ||| 332| Reconstruct Itinerary | C++ Python | O(t! / (n1! * n2! * ... nk!)) | O(t) | Medium ||| 339| Nested List Weight Sum | C++ Python | O(n) | O(h) | Easy |📖|| 364| Nested List Weight Sum II | C++ Python | O(n) | O(h) | Medium |📖|| 366| Find Leaves of Binary Tree | C++ Python | O(n) | O(h) | Medium |📖|| 399| Evaluate Division | C++ Python | O(q * |V|!) | O(e) | Medium ||| 417 | Pacific Atlantic Water Flow | C++ Python | O(m * n) | O(m * n) | Medium || 440| K-th Smallest in Lexicographical Order | C++ Python | O(logn) | O(logn) | Hard || 464| Can I Win | C++ Python | O(n!) | O(n) | Medium ||

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 17| Letter Combinations of a Phone Number| Python | O(n * 4^n) | O(n) | Medium || 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(k * n^k) | O(k) | Medium || 40| Combination Sum II| Python| O(k * C(n, k))| O(k) | Medium || 46| Permutations| Python | O(n * n!) | O(n) | Medium || 47| Permutations II| Python | O(n * n!) | O(n) | 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(1) | O(1) | Medium || 78| Subsets | C++ Python | O(n * 2^n) | O(1) | Medium || 90| Subsets II | C++ Python | O(n * 2^n) | O(1) | Medium || 126| Word Ladder II |Python | O(n * d) | O(d) | Hard || 131| Palindrome Partitioning | Python | O(n^2) ~ O(2^n) | O(n^2) | Medium || 140| Word Break II | C++ Python | O(n * l^2 + n * r) | O(n^2) | Hard || 212| Word Search II | C++ Python | O(m * n * l) | O(l) | Hard | LintCode | Trie, DFS 216| Combination Sum III| C++ Python | O(k * C(n, k)) | O(k) | Medium || 254| Factor Combinations | C++ Python | O(nlogn) | O(logn) | Medium |📖|| 267| Palindrome Permutation II | C++ Python | O(n * n!) | O(n) | Medium |📖|| 291| Word Pattern II | C++ Python | O(n * C(n - 1, c - 1)) | O(n + c) | Hard |📖|| 294| Flip Game II | C++ Python | O(n + c^2) | O(c) | Medium |📖| DP, Hash | 320| Generalized Abbreviation | C++ Python | O(n * 2^n) | O(n) | Medium |📖|| 425| Word Squares | C++ Python | O(n^2 * n!) | O(n^2) | Hard |📖||

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 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 || 87| Scramble String | Python | O(n^4) | O(n^3) | Hard || 91| Decode Ways | C++ Python| O(n) | O(1) | Medium || 96| Unique Binary Search Trees | Python | O(n) | O(1) | Medium || Math 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 | C++ Python | O(n * l^2) | O(n) | Medium || 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 || 221| Maximal Square| C++ Python | O(n^2) | O(n) | Medium | EPI | 256| Paint House | C++ Python | O(n)| O(1)| Medium |📖|| 265| Paint House II | C++ Python | O(n * k)| O(k)| Hard |📖|| 276| Paint Fence | C++ Python | O(n)| O(1)| Easy |📖|| 279| Perfect Squares| C++ Python | O(n * sqrt(n)) | O(n) | Medium || Hash | 303| Range Sum Query - Immutable| C++ Python | ctor: O(n), lookup: O(1) | O(n) | Easy || 304| Range Sum Query 2D - Immutable| C++ Python | ctor: O(m * n), lookup: O(1) | O(m * n) | Medium || 309| Best Time to Buy and Sell Stock with Cooldown | C++ Python | O(n) | O(1) | Medium || 312| Burst Balloons | C++ Python | O(n^3) | O(n^2) | Hard || 322| Coin Change | C++ Python | O(n * k) | O(k) | Medium || 351| Android Unlock Patterns | C++ Python | O(9^2 * 2^9) | O(9 * 2^9) | Medium | 📖 | Backtracking | 357| Count Numbers with Unique Digits | C++ Python | O(n) | O(1) | Medium || Backtracking, Math | 361| Bomb Enemy | C++ Python | O(m * n) | O(m * n) | Medium | 📖 | | 368| Largest Divisible Subset | C++ Python | O(n^2) | O(n) | Medium | | | 375| Guess Number Higher or Lower II| C++ Python | O(n^2) | O(n^2) | Medium | | 377| Combination Sum IV| C++ Python | O(nlogn + n * t) | O(t) | Medium | | 403 | Frog Jump | C++ Python | O(n) | O(n) ~ O(n^2) | Hard || 416 | Partition Equal Subset Sum | C++ Python | O(n * s) | O(s) | Medium || 418 | Sentence Screen Fitting | C++ Python | O(r + n * c) | O(n) | Medium |📖| 446 | Arithmetic Slices II - Subsequence | C++ Python | O(n^2) | O(n * d) | Hard || 465 | Optimal Account Balancing | C++ Python | O(n * 2^n) | O(n * 2^n) | Hard |📖| 466 | Count The Repetitions | C++ Python | O(s1 * min(s2, n1)) | O(s2) | Hard || 467 | Unique Substrings in Wraparound String | C++ Python | O(n) | O(1) | Medium || 471 | Encode String with Shortest Length | C++ Python | O(n^3) on average | O(n^2) | Medium |📖| 472 | Concatenated Words | C++ Python | O(n * l^2) | O(n * l) | Medium || 474 | Ones and Zeroes | C++ Python | O(s * m * n) | O(m * n) | Medium ||

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 11| Container With Most Water| C++ Python | O(n) | O(1) | Medium || 42| Trapping Rain Water | C++ 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 || 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| C++ Python | O(n) | O(n) | Hard || 316| Remove Duplicate Letters | C++ Python | O(n)| O(k)| Hard || Ascending Stack | 321| Create Maximum Number| C++ Python | O(k * (m + n + k)) ~ O(k * (m + n + k^2))| O(m + n + k^2) | Hard | variant of Delete Digits | Greedy, DP 330| Patching Array | C++ Python | O(s + logn) | O(1) | Hard || 376| Wiggle Subsequence| C++ Python | O(n) | O(1) | Medium || 392| Is Subsequence| C++ Python | O(n) | O(1) | Medium || 397| Integer Replacement| C++ Python | O(n) | O(1) | Medium || Math 402 | Remove K Digits | C++ Python | O(n) | O(n) | Medium | LintCode | 435 | Non-overlapping Intervals | C++ Python | O(nlogn) | O(1) | Medium | | 452 | Minimum Number of Arrows to Burst Balloons | C++ Python | O(nlogn) | O(1) | Medium | | 455 | Assign Cookies | C++ Python | O(nlogn) | O(1) | Easy | |

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 284| Peeking Iterator| C++ Python | O(1) | O(1) | Medium || 348| Design Tic-Tac-Toe | C++ Python | O(1)| O(n^2)| Medium |📖|| 353| Design Snake Game | C++ Python | O(1)| O(s)| Medium |📖| Deque | 355| Design Twitter | C++ Python | O(klogu)| O(t + f)| Medium | LintCode | Heap | 359| Logger Rate Limiter | C++ Python | O(1), amortized | O(k)| Easy |📖| Deque | 362| Design Hit Counter | C++ Python | O(1), amortized | O(k)| Medium |📖| Deque | 379| Design Phone Directory | C++ Python | O(1) | O(n)| Medium |📖| | 380| Insert Delete GetRandom O(1) | C++ Python | O(1) | O(n)| Hard || | 381| Insert Delete GetRandom O(1) - Duplicates allowed | C++ Python | O(1) | O(n)| Hard || | 432| All O`one Data Structure | C++ Python | O(1) | O(n)| Hard || | 460| LFU Cache | C++ Python | O(1) | O(k)| Hard || |

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 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 || 262| Trips and Users | MySQL | O((t * u) + tlogt) | O(t) | Hard ||

-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------| ----- 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 ||