README.md

LeetCode by Swift

[LeetCode Online Judge] (https://leetcode.com/) is a website containing many algorithm questions. Most of them are real interview questions of Google, Facebook, LinkedIn, Apple, etc. This repo shows my solutions by Swift with the code style strictly follows the RayWenderlich Swift Style Guide. Please feel free to reference and STAR to support this repo, thank you!

Data Structures

• Array
• String
• Linked List
• Stack
• Tree
• Dynamic programming
• Depth-first search
• Math
• Search
• Sort
• Union Find

Companies

• Google
• Facebook
• Snapchat
• Uber
• Airbnb
• LinkedIn
• Amazon
• Microsoft

Progress

Problem Status shows the latest progress to all 700+ questions. Currently we have 222 completed solutions. Note: questions with ♥ mark means that you have to Subscript to premium membership of LeetCode to unlock them. Thank you for great contributions from CharleneJiang, ReadmeCritic, demonkoo, DaiYue, Quaggie and jindulys.

Array

Title Solution Difficulty Time Space Max Consecutive Ones Swift Easy O(n) O(1) Heaters Swift Easy O(nlogn) O(1) Number of Boomerangs Swift Easy O(n ^ 2) O(n) Island Perimeter Swift Easy O(nm) O(1) Majority Element Swift Easy O(n) O(1) Majority Element II Swift Medium O(n) O(1) Intersection of Two Arrays Swift Easy O(n) O(n) Intersection of Two Arrays II Swift Easy O(nlogn) O(n) Contains Duplicate Swift Easy O(n) O(n) Contains Duplicate II Swift Easy O(n) O(n) Remove Duplicates from Sorted Array Swift Easy O(n) O(1) Remove Duplicates from Sorted Array II Swift Medium O(n) O(1) Move Zeroes Swift Easy O(n) O(1) Remove Element Swift Easy O(n) O(1) Two Sum Swift Easy O(n) O(n) 3Sum Swift Medium O(n^2) O(nC3) 3Sum Closest Swift Medium O(n^2) O(nC3) 4Sum Swift Medium O(n^3) O(nC4) Summary Ranges Swift Medium O(n) O(n) Shortest Word Distance Swift Easy O(n) O(1) Shortest Word Distance III Swift Medium O(n) O(1) Maximum Size Subarray Sum Equals k Swift Easy O(n) O(n) Product of Array Except Self Swift Medium O(n) O(n) Rotate Array Swift Easy O(n) O(1) Rotate Image Swift Medium O(n^2) O(1) Spiral Matrix Swift Medium O(n^2) O(1) Spiral Matrix II Swift Medium O(n^2) O(1) Valid Sudoku Swift Easy O(n^2) O(n) Set Matrix Zero Swift Medium O(n^2) O(1) Next Permutation Swift Medium O(n) O(1) Gas Station Swift Medium O(n) O(1) Game of Life Swift Medium O(n) O(1) Sliding Window Maximum Swift Hard O(n) O(n) Longest Consecutive Sequence Swift Hard O(n) O(n)

String

Title Solution Difficulty Time Space Fizz Buzz Swift Easy O(n) O(1) First Unique Character in a String Swift Easy O(n) O(1) Keyboard Row Swift Easy O(nm) O(n) Valid Palindrome Swift Easy O(n) O(n) Detect Capital Swift Easy O(n) O(1) Count and Say Swift Easy O(n^2) O(n) Flip Game Swift Easy O(n) O(n) Implement strStr() Swift Easy O(nm) O(n) Isomorphic Strings Swift Easy O(n) O(n) Reverse String Swift Easy O(n) O(n) Reverse String II Swift Easy O(n) O(n) Reverse Vowels of a String Swift Easy O(n) O(n) Length of Last Word Swift Easy O(n) O(n) Add Strings Swift Easy O(n) O(1) Multiply Strings Swift Medium O(n) O(1) Palindrome Permutation Swift Easy O(n) O(n) Valid Anagram Swift Easy O(nlogn) O(1) Ransom Note Swift Easy O(n) O(n) Group Anagrams Swift Medium O(nmlogm + nlogn) O(n) Longest Common Prefix Swift Easy O(nm) O(m) Longest Substring Without Repeating Characters Swift Medium O(n) O(n) One Edit Distance Swift Medium O(n) O(n) Word Pattern Swift Easy O(n) O(n) Minimum Window Substring Swift Hard O(n^2) O(n) Text Justification Swift Hard O(n) O(n)

Linked List

Title Solution Difficulty Time Space Reverse Linked List Swift Easy O(n) O(1) Palindrome Linked List Swift Easy O(n) O(1) Swap Nodes in Pairs Swift Easy O(n) O(1) Remove Linked List Elements Swift Easy O(n) O(1) Remove Duplicates from Sorted List Swift Easy O(n) O(1) Remove Duplicates from Sorted List II Swift Medium O(n) O(1) Remove Nth Node From End of List Swift Easy O(n) O(1) Odd Even Linked List Swift Medium O(n) O(1) Rotate List Swift Medium O(n) O(1) Reorder List Swift Medium O(n) O(1) Merge Two Sorted Lists Swift Easy O(n) O(1) Merge k Sorted Lists Swift Hard O(mlogn) O(1) Partition List Swift Medium O(n) O(1)

Stack

Title Solution Difficulty Time Space Valid Parentheses Swift Easy O(n) O(n) Longest Valid Parentheses Swift Hard O(n) O(n) Evaluate Reverse Polish Notation Swift Medium O(n) O(n) Simplify Path Swift Medium O(n) O(n) Remove K Digits Swift Medium O(n) O(n) Ternary Expression Parser Swift Medium O(n) O(n) Binary Tree Preorder Traversal Swift Medium O(n) O(n) Binary Tree Inorder Traversal Swift Medium O(n) O(n) Binary Tree Postorder Traversal Swift Hard O(n) O(n)

Tree

Title Solution Difficulty Time Space Same Tree Swift Easy O(n) O(n) Symmetric Tree Swift Easy O(n) O(n) Invert Binary Tree Swift Easy O(n) O(n) Binary Tree Upside Down Swift Medium O(n) O(1) Minimum Depth of Binary Tree Swift Easy O(n) O(n) Maximum Depth of Binary Tree Swift Easy O(n) O(n) Balanced Binary Tree Swift Easy O(n) O(n) Sum of Left Leaves Swift Easy O(n) O(1) Flatten Binary Tree to Linked List Swift Medium O(n) O(1) Validate Binary Search Tree Swift Medium O(n) O(n) Binary Tree Level Order Traversal Swift Easy O(n) O(n) Binary Tree Level Order Traversal II Swift Easy O(n) O(n) Binary Tree Zigzag Level Order Traversal Swift Medium O(n) O(n) Binary Tree Vertical Order Traversal Swift Medium O(n) O(n) Binary Tree Right Side View Swift Medium O(n) O(n) Construct Binary Tree from Preorder and Inorder Traversal Swift Medium O(n) O(n) Construct Binary Tree from Inorder and Postorder Traversal Swift Medium O(n) O(n) Path Sum Swift Easy O(n) O(n) Path Sum II Swift Medium O(n) O(n) Path Sum III Swift Easy O(n^2) O(1) Unique Binary Search Trees Swift Medium O(n^2) O(n) Recover Binary Search Tree Swift Hard O(n) O(1) Merge Two Binary Trees Swift Easy O(n) O(n)

Dynamic programming

Title Solution Difficulty Time Space Nested List Weight Sum Swift Easy O(n) O(1) Climbing Stairs Swift Easy O(n) O(1) Unique Paths Swift Medium O(mn) O(mn) Unique Paths II Swift Medium O(mn) O(mn) Decode Ways Swift O(n) O(n)

Minimum Path Sum Swift Medium O(mn) O(mn) Generate Parentheses Swift Medium O(n^2) O(n) Different Ways to Add Parentheses Swift Medium O(n^n) O(n) Best Time to Buy and Sell Stock Swift Easy O(n) O(1) Best Time to Buy and Sell Stock II Swift Medium O(n) O(1) Best Time to Buy and Sell Stock III Swift Hard O(n) O(n) Best Time to Buy and Sell Stock IV Swift Hard O(n^2) O(n) Best Time to Buy and Sell Stock with Cooldown Swift Medium O(n^2) O(n) Coin Change Swift Medium O(n^2) O(n) Longest Increasing Subsequence Swift Medium O(n^2) O(n) Longest Palindromic Substring Swift Medium O(n^2) O(n^2) Perfect Squares Swift Medium O(n^2) O(n) House Robber Swift Easy O(n) O(1) House Robber II Swift Medium O(n) O(1) Paint Fence Swift Easy O(n) O(n) Maximum Subarray Swift Medium O(n) O(1) Maximum Product Subarray Swift Medium O(n) O(1) Maximal Square Swift Medium O(mn) O(mn) Edit Distance Swift Hard O(mn) O(mn) Combination Sum IV Swift Medium O(2^n) O(n) Triangle Swift Medium O(2^n - 1) O(m) Guess Number Higher or Lower II Swift Medium O(nlogn) O(n^2) Burst Ballons Swift Hard O(n^3) O(n) Frog Jump Swift Hard O(n^2) O(n)

Depth-first search

Title Solution Difficulty Time Space Permutations Swift Medium O(n!) O(n) Permutations II Swift Medium O(n!) O(n) Subsets Swift Medium O(n!) O(n) Subsets II Swift Medium O(n!) O(n) Combinations Swift Medium O(n!) O(n) Combination Sum Swift Medium O(n^n) O(2^n - 1) Combination Sum II Swift Medium O(n!) O(2^n - 2) Combination Sum III Swift Medium O(n!) O(nCk) Letter Combinations of a Phone Number Swift Medium O(mn) O(n) Factor Combinations Swift Medium O(n^n)) O(2^n - 1) Generalized Abbreviation Swift Medium O(n!) O(2^n) Palindrome Partitioning Swift Medium O(n!) O(n) Number of Islands Swift Medium O((mn)^2) O(1) Walls and Gates Swift Medium O(n!) O(2^n) Word Search Swift Medium O((n^2)!) O(n^2) Word Search II Swift Hard O(((mn)^2)) O(n^2) N-Queens Swift Hard O((n^4)) O(n^2) N-Queens II Swift Hard O((n^3)) O(n) Sudoku Solver Swift Hard O(n^4) O(1) Remove Invalid Parentheses Swift Hard O(n!) O(n) Expression Add Operators Swift Hard O(n!) O(n)

Math

Title Solution Difficulty Time Space Add Binary Swift Easy O(n) O(n) Add Two Numbers Swift Medium O(n) O(1) Add Digits Swift Easy O(1) O(1) Plus One Swift Easy O(n) O(1) Number Complement Swift Easy O(n) O(1) Hamming Distance Swift Easy O(n) O(1) Integer Break Swift Medium O(logn) O(1) Happy Number Swift Easy O(n) O(n) Single Number Swift Medium O(n) O(1) Ugly Number Swift Easy O(logn) O(1) Ugly Number II Swift Medium O(n) O(n) Super Ugly Number Swift Medium O(n^2) O(n) Count Primes Swift Easy O(n) O(n) String to Integer (atoi) Swift Easy O(n) O(1) Pow(x, n) Swift Medium O(logn) O(1) Power of Two Swift Easy O(1) O(1) Power of Three Swift Easy O(1) O(1) Super Power Swift Medium O(n) O(1) Sum of Two Integers Swift Easy O(n) O(1) Reverse Integer Swift Easy O(n) O(1) Excel Sheet Column Number Swift Easy O(n) O(1) Integer to Roman Swift Medium O(n) O(1) Roman to Integer Swift Easy O(n) O(n) Integer to English Words Swift Hard O(n) O(1) Rectangle Area Swift Easy O(1) O(1) Trapping Rain Water Swift Hard O(n) O(n) Container With Most Water Swift Medium O(n) O(1) Counting Bits Swift Medium O(n) O(n) K-th Smallest in Lexicographical Order Swift Hard O(n) O(1)

Search

Title Solution Difficulty Time Space Closest Binary Search Tree Value Swift Easy O(logn) O(1) Closest Binary Search Tree Value II Swift Hard O(n) O(n) Search in Rotated Sorted Array Swift Hard O(logn) O(1) Search in Rotated Sorted Array II Swift Medium O(logn) O(1) Find Minimum in Rotated Sorted Array Swift Medium O(logn) O(1) Find Minimum in Rotated Sorted Array II Swift Hard O(logn) O(1) Search a 2D Matrix Swift Medium O(log(m + n)) O(1) Search a 2D Matrix II Swift Medium O(m + n) O(1) Search for a Range Swift Medium O(logn) O(1) Search Insert Position Swift Medium O(logn) O(1) Find Peak Element Swift Medium O(logn) O(1) Sqrt(x) Swift Medium O(logn) O(1) Median of Two Sorted Arrays Swift Hard O(log(m + n)) O(1)

Sort

Title Solution Difficulty Time Space Merge Sorted Array Swift Easy O(n) O(1) Sort Colors Swift Medium O(n) O(1) Wiggle Sort Swift Medium O(n) O(1) Wiggle Sort II Swift Medium O(nlogn) O(n) Sort Transformed Array Swift Medium O(n) O(1) Top K Frequent Elements Swift Medium O(nlogn) O(n) Meeting Rooms Swift Easy O(nlogn) O(1) Meeting Rooms II Swift Medium O(nlogn) O(n) Merge Intervals Swift Hard O(nlogn) O(n) Alien Dictionary Swift Hard O(nm) O(nm) Array Partition I Swift Easy O(nlogn) O(n)

Union Find

Title Solution Difficulty Time Space Number of Connected Components in an Undirected Graph Swift Medium O(nlogn) O(n) Graph Valid Tree Swift Medium O(nlogn) O(n)

Google

Title Solution Difficulty Frequency Plus One Swift Easy ★★★★★★ Number of Islands Swift Medium ★★★★ Summary Ranges Swift Medium ★★★★ Perfect Squares Swift Medium ★★★★ Merge Intervals Swift Hard ★★★ Valid Parentheses Swift Easy ★★★ Trapping Rain Water Swift Hard ★★ Merge k Sorted Lists Swift Hard ★★ Longest Consecutive Sequence Swift Hard ★★ Find Peak Element Swift Medium ★★ Power of Two Swift Easy ★★ Spiral Matrix Swift Medium ★★ Sliding Window Maximum Swift Hard ★★ Pow(x, n) Swift Medium ★★ Letter Combinations of a Phone Number Swift Medium ★★ Heaters Swift Easy ★

Facebook

Title Solution Difficulty Frequency 3Sum Swift Medium ★★★★★★ Move Zeroes Swift Easy ★★★★★★ Remove Invalid Parentheses Swift Hard ★★★★★★ Add Binary Swift Easy ★★★★★ Two Sum Swift Easy ★★★★★ Letter Combinations of a Phone Number Swift Medium ★★★★ Merge k Sorted Lists Swift Hard ★★★★ Reverse Linked List Swift Easy ★★★ Merge Intervals Swift Hard ★★★ Number of Islands Swift Medium ★★★ Reverse Linked List Swift Easy ★★★ Expression Add Operators Swift Hard ★★★ Subsets Swift Medium ★★★ Sort Colors Swift Medium ★★

Snapchat

Title Solution Difficulty Frequency Game of Life Swift Medium ★★★★★★ Meeting Rooms II Swift Medium ★★★★★★ Valid Sudoku Swift Easy ★★★★★ Binary Tree Vertical Order Traversal Swift Medium ★★★★ Alien Dictionary Swift Hard ★★★★ One Edit Distance Swift Medium ★★★ Sudoku Solver Swift Hard ★★★ Reverse Linked List Swift Easy ★★ Unique Binary Search Trees Swift Medium ★★ Minimum Window Substring Swift Hard ★★ Remove K Digits Swift Medium ★ Ternary Expression Parser Swift Medium ★

Uber

Title Solution Difficulty Frequency Valid Sudoku Swift Easy ★★★★ Spiral Matrix Swift Medium ★★★★ Letter Combinations of a Phone Number Swift Medium ★★★★ Group Anagrams Swift Medium ★★★★ Word Pattern Swift Easy ★★★ Roman to Integer Swift Easy ★★★ Combination Sum Swift Medium ★★

Airbnb

Title Solution Difficulty Frequency Two Sum Swift Easy ★★★★★ Text Justification Swift Hard ★★★★ House Robber Swift Easy ★★ Single Number Swift Medium ★★ Word Search II Swift Hard ★★ Add Two Numbers Swift Medium ★★

LinkedIn

Title Solution Difficulty Frequency Maximum Subarray Swift Medium ★★★★★★ Pow(x, n) Swift Medium ★★★★★★ Merge Intervals Swift Hard ★★★★★★ Isomorphic Strings Swift Easy ★★★★★★ Search in Rotated Sorted Array Swift Hard ★★★★★ Search for a Range Swift Medium ★★★★★ Two Sum Swift Easy ★★★★ Binary Tree Level Order Traversal Swift Easy ★★★★ Evaluate Reverse Polish Notation Swift Medium ★★★ Maximum Product Subarray Swift Medium ★★★ Product of Array Except Self Swift Medium ★★★ Symmetric Tree Swift Easy ★★

Amazon

Title Solution Difficulty Frequency Two Sum Swift Easy ★★★★★★ Number of Islands Swift Medium ★★ Add Two Numbers Swift Medium ★★ Reverse Linked List Swift Easy ★★ Valid Parentheses Swift Easy ★★ Longest Palindromic Substring Swift Medium ★★ Trapping Rain Water Swift Hard ★★ Longest Substring Without Repeating Characters Swift Medium ★★ Letter Combinations of a Phone Number Swift Medium ★★ Valid Anagram Swift Easy ★★ Rotate Image Swift Medium ★★ Best Time to Buy and Sell Stock Swift Easy ★★ 3Sum Swift Medium ★★ Sliding Window Maximum Swift Hard ★★

Microsoft

Title Solution Difficulty Frequency Reverse Linked List Swift Easy ★★★★★★ Two Sum Swift Easy ★★★★★ String to Integer (atoi) Swift Easy ★★★★ Add Two Numbers Swift Medium ★★★★ Excel Sheet Column Number Swift Easy ★★★★ Validate Binary Search Tree Swift Medium ★★★ Merge Two Sorted Lists Swift Easy ★★★

Problem Status

Solution Number Title Difficulty Swift 377 Combination Sum IV Medium

376 Wiggle Subsequence Medium Swift 375 Guess Number Higher or Lower II Medium

374 Guess Number Higher or Lower Easy

373 Find K Pairs with Smallest Sums Medium Swift 372 Super Pow Medium Swift 371 Sum of Two Integers Easy

370 Range Addition ♥ Medium

369 Plus One Linked List ♥ Medium

368 Largest Divisible Subset Medium

367 Valid Perfect Square Medium

366 Find Leaves of Binary Tree ♥ Medium

365 Water and Jug Problem Medium

364 Nested List Weight Sum II ♥ Medium

363 Max Sum of Rectangle No Larger Than K Hard

362 Design Hit Counter ♥ Medium

361 Bomb Enemy ♥ Medium Swift 360 Sort Transformed Array ♥ Medium

359 Logger Rate Limiter ♥ Easy

358 Rearrange String k Distance Apart ♥ Hard

357 Count Numbers with Unique Digits Medium

356 Line Reflection ♥ Medium

355 Design Twitter Medium

354 Russian Doll Envelopes Hard

353 Design Snake Game ♥ Medium

352 Data Stream as Disjoint Intervals Hard

351 Android Unlock Patterns ♥ Medium Swift 350 Intersection of Two Arrays II Easy Swift 349 Intersection of Two Arrays Easy

348 Design Tic-Tac-Toe ♥ Medium Swift 347 Top K Frequent Elements Medium

346 Moving Average from Data Stream ♥ Easy Swift 345 Reverse Vowels of a String Easy Swift 344 Reverse String Easy Swift 343 Integer Break Medium

342 Power of Four Easy

341 Flatten Nested List Iterator Medium

340 Longest Substring with At Most K Distinct Characters ♥ Hard Swift 339 Nested List Weight Sum ♥ Easy Swift 338 Counting Bits Medium

337 House Robber III Medium

336 Palindrome Pairs Hard

335 Self Crossing Hard

334 Increasing Triplet Subsequence Medium

333 Largest BST Subtree ♥ Medium

332 Reconstruct Itinerary Medium

331 Verify Preorder Serialization of a Binary Tree Medium

330 Patching Array Hard

329 Longest Increasing Path in a Matrix Hard Swift 328 Odd Even Linked List Medium

327 Count of Range Sum Hard Swift 326 Power of Three Easy Swift 325 Maximum Size Subarray Sum Equals k ♥ Medium Swift 324 Wiggle Sort II Medium Swift 323 Number of Connected Components in an Undirected Graph ♥ Medium Swift 322 Coin Change Medium

321 Create Maximum Number Hard Swift 320 Generalized Abbreviation ♥ Medium

319 Bulb Switcher Medium

318 Maximum Product of Word Lengths Medium

317 Shortest Distance from All Buildings ♥ Hard

316 Remove Duplicate Letters Hard

315 Count of Smaller Numbers After Self Hard Swift 314 Binary Tree Vertical Order Traversal ♥ Medium Swift 313 Super Ugly Number Medium Swift 312 Burst Balloons Hard

311 Sparse Matrix Multiplication ♥ Medium

310 Minimum Height Trees Medium Swift 309 Best Time to Buy and Sell Stock with Cooldown Medium

308 Range Sum Query 2D - Mutable ♥ Hard

307 Range Sum Query - Mutable Medium

306 Additive Number Medium

305 Number of Islands II ♥ Hard

304 Range Sum Query 2D - Immutable Medium

303 Range Sum Query - Immutable Easy

302 Smallest Rectangle Enclosing Black Pixels ♥ Hard Swift 301 Remove Invalid Parentheses Hard Swift 300 Longest Increasing Subsequence Medium

299 Bulls and Cows Easy

298 Binary Tree Longest Consecutive Sequence ♥ Medium

297 Serialize and Deserialize Binary Tree Hard Swift 296 Best Meeting Point ♥ Hard

295 Find Median from Data Stream Hard

294 Flip Game II ♥ Medium Swift 293 Flip Game ♥ Easy

292 Nim Game Easy

291 Word Pattern II ♥ Hard Swift 290 Word Pattern Easy Swift 289 Game of Life Medium

288 Unique Word Abbreviation ♥ Easy

287 Find the Duplicate Number Hard Swift 286 Walls and Gates ♥ Medium

285 Inorder Successor in BST ♥ Medium

284 Peeking Iterator Medium Swift 283 Move Zeroes Easy Swift 282 Expression Add Operators Hard

281 Zigzag Iterator ♥ Medium Swift 280 Wiggle Sort ♥ Medium Swift 279 Perfect Squares Medium

278 First Bad Version Easy

277 Find the Celebrity ♥ Medium Swift 276 Paint Fence ♥ Easy

275 H-Index II Medium

274 H-Index Medium Swift 273 Integer to English Words Hard Swift 272 Closest Binary Search Tree Value II ♥ Hard

271 Encode and Decode Strings ♥ Medium Swift 270 Closest Binary Search Tree Value ♥ Easy Swift 269 Alien Dictionary ♥ Hard

268 Missing Number Medium

267 Palindrome Permutation II ♥ Medium Swift 266 Palindrome Permutation ♥ Easy

265 Paint House II ♥ Hard Swift 264 Ugly Number II Medium Swift 263 Ugly Number Easy Swift 261 Graph Valid Tree ♥ Medium

260 Single Number III Medium

259 3Sum Smaller ♥ Medium Swift 258 Add Digits Easy

257 Binary Tree Paths Easy

256 Paint House ♥ Medium

255 Verify Preorder Sequence in Binary Search Tree ♥ Medium Swift 254 Factor Combinations ♥ Medium Swift 253 Meeting Rooms II ♥ Medium Swift 252 Meeting Rooms ♥ Easy

251 Flatten 2D Vector ♥ Medium

250 Count Univalue Subtrees ♥ Medium

249 Group Shifted Strings ♥ Easy

248 Strobogrammatic Number III ♥ Hard

247 Strobogrammatic Number II ♥ Medium

246 Strobogrammatic Number ♥ Easy Swift 245 Shortest Word Distance III ♥ Medium

244 Shortest Word Distance II ♥ Medium Swift 243 Shortest Word Distance ♥ Easy Swift 242 Valid Anagram Easy Swift 241 Different Ways to Add Parentheses Medium Swift 240 Search a 2D Matrix II Medium Swift 239 Sliding Window Maximum Hard Swift 238 Product of Array Except Self Medium

237 Delete Node in a Linked List Easy

236 Lowest Common Ancestor of a Binary Tree Medium

235 Lowest Common Ancestor of a Binary Search Tree Easy Swift 234 Palindrome Linked List Easy

233 Number of Digit One Hard

232 Implement Queue using Stacks Easy Swift 231 Power of Two Easy

230 Kth Smallest Element in a BST Medium Swift 229 Majority Element II Medium Swift 228 Summary Ranges Medium

227 Basic Calculator II Medium Swift 226 Invert Binary Tree Easy

225 Implement Stack using Queues Easy

224 Basic Calculator Hard Swift 223 Rectangle Area Easy

222 Count Complete Tree Nodes Medium Swift 221 Maximal Square Medium

220 Contains Duplicate III Medium Swift 219 Contains Duplicate II Easy

218 The Skyline Problem Hard Swift 217 Contains Duplicate Easy Swift 216 Combination Sum III Medium

215 Kth Largest Element in an Array Medium

214 Shortest Palindrome Hard Swift 213 House Robber II Medium Swift 212 Word Search II Hard

211 Add and Search Word - Data structure design Medium

210 Course Schedule II Medium

209 Minimum Size Subarray Sum Medium

208 Implement Trie (Prefix Tree) Medium

207 Course Schedule Medium Swift 206 Reverse Linked List Easy Swift 205 Isomorphic Strings Easy Swift 204 Count Primes Easy Swift 203 Remove Linked List Elements Easy Swift 202 Happy Number Easy

201 Bitwise AND of Numbers Range Medium Swift 200 Number of Islands Medium Swift 199 Binary Tree Right Side View Medium Swift 198 House Robber Easy

191 Number of 1 Bits Easy

190 Reverse Bits Easy Swift 189 Rotate Array Easy Swift 188 Best Time to Buy and Sell Stock IV Hard

187 Repeated DNA Sequences Medium

186 Reverse Words in a String II ♥ Medium

179 Largest Number Medium

174 Dungeon Game Hard

173 Binary Search Tree Iterator Medium

172 Factorial Trailing Zeroes Easy Swift 171 Excel Sheet Column Number Easy

170 Two Sum III - Data structure design ♥ Easy Swift 169 Majority Element Easy

168 Excel Sheet Column Title Easy

167 Two Sum II - Input array is sorted ♥ Medium

166 Fraction to Recurring Decimal Medium

165 Compare Version Numbers Easy

164 Maximum Gap Hard

163 Missing Ranges ♥ Medium Swift 162 Find Peak Element Medium Swift 161 One Edit Distance♥ Medium

160 Intersection of Two Linked Lists Easy

159 Longest Substring with At Most Two Distinct Characters ♥ Hard

158 Read N Characters Given Read4 II - Call multiple times ♥ Hard

157 Read N Characters Given Read4 ♥ Easy Swift 156 Binary Tree Upside Down ♥ Medium

155 Min Stack Easy Swift 154 Find Minimum in Rotated Sorted Array II Hard Swift 153 Find Minimum in Rotated Sorted Array Medium Swift 152 Maximum Product Subarray Medium

151 Reverse Words in a String Medium Swift 150 Evaluate Reverse Polish Notation Medium

149 Max Points on a Line Hard

148 Sort List Medium

147 Insertion Sort List Medium

146 LRU Cache Hard Swift 145 Binary Tree Postorder Traversal Hard Swift 144 Binary Tree Preorder Traversal Medium Swift 143 Reorder List Medium

142 Linked List Cycle II Medium

141 Linked List Cycle Easy

140 Word Break II Hard

139 Word Break Medium

138 Copy List with Random Pointer Hard Swift 137 Single Number II Medium Swift 136 Single Number Medium

135 Candy Hard Swift 134 Gas Station Medium

133 Clone Graph Medium

132 Palindrome Partitioning II Hard Swift 131 Palindrome Partitioning Medium

130 Surrounded Regions Medium

129 Sum Root to Leaf Numbers Medium Swift 128 Longest Consecutive Sequence Hard

127 Word Ladder Medium

126 Word Ladder II Hard Swift 125 Valid Palindrome Easy

124 Binary Tree Maximum Path Sum Hard Swift 123 Best Time to Buy and Sell Stock III Hard Swift 122 Best Time to Buy and Sell Stock II Medium Swift 121 Best Time to Buy and Sell Stock Easy Swift 120 Triangle Medium

119 Pascal's Triangle II Easy

118 Pascal's Triangle Easy

117 Populating Next Right Pointers in Each Node II Hard

116 Populating Next Right Pointers in Each Node Medium

115 Distinct Subsequences Hard Swift 114 Flatten Binary Tree to Linked List Medium Swift 113 Path Sum II Medium Swift 112 Path Sum Easy Swift 111 Minimum Depth of Binary Tree Easy Swift 110 Balanced Binary Tree Easy

109 Convert Sorted List to Binary Search Tree Medium

108 Convert Sorted Array to Binary Search Tree Medium Swift 107 Binary Tree Level Order Traversal II Easy Swift 106 Construct Binary Tree from Inorder and Postorder Traversal Medium Swift 105 Construct Binary Tree from Preorder and Inorder Traversal Medium Swift 104 Maximum Depth of Binary Tree Easy Swift 103 Binary Tree Zigzag Level Order Traversal Medium Swift 102 Binary Tree Level Order Traversal Easy Swift 101 Symmetric Tree Easy Swift 100 Same Tree Easy Swift 99 Recover Binary Search Tree Hard Swift 98 Validate Binary Search Tree Medium

97 Interleaving String Hard Swift 96 Unique Binary Search Trees Medium

95 Unique Binary Search Trees II Medium Swift 94 Binary Tree Inorder Traversal Medium

93 Restore IP Addresses Medium

92 Reverse Linked List II Medium (./DP/DecodeWays.swift) 91 Decode Ways Medium Swift 90 Subsets II Medium

89 Gray Code Medium Swift 88 Merge Sorted Array Easy

87 Scramble String Hard Swift 86 Partition List Medium

85 Maximal Rectangle Hard

84 Largest Rectangle in Histogram Hard Swift 83 Remove Duplicates from Sorted List Easy Swift 82 Remove Duplicates from Sorted List II Medium Swift 81 Search in Rotated Sorted Array II Medium Swift 80 Remove Duplicates from Sorted Array II Medium Swift 79 Word Search Medium Swfit 78 Subsets Medium Swift 77 Combinations Medium Swift 76 Minimum Window Substring Hard Swift 75 Sort Colors Medium Swift 74 Search a 2D Matrix Medium Swift 73 Set Matrix Zeroes Medium Swift 72 Edit Distance Hard Swift 71 Simplify Path Medium Swift 70 Climbing Stairs Easy Swift 69 Sqrt(x) Medium Swift 68 Text Justification Hard Swift 67 Add Binary Easy Swift 66 Plus One Easy

65 Valid Number Hard Swift 64 Minimum Path Sum Medium Swift 63 Unique Paths II Medium Swift 62 Unique Paths Medium Swift 61 Rotate List Medium

60 Permutation Sequence Medium Swift 59 Spiral Matrix II Medium Swift 58 Length of Last Word Easy

57 Insert Interval Hard Swift 56 Merge Intervals Hard

55 Jump Game Medium Swift 54 Spiral Matrix Medium Swift 53 Maximum Subarray Medium Swift 52 N-Queens II Hard Swift 51 N-Queens Hard Swift 50 "Pow(x, n)" Medium Swift 49 Group Anagrams Medium Swift 48 Rotate Image Medium Swift 47 Permutations II Medium Swift 46 Permutations Medium

45 Jump Game II Hard

44 Wildcard Matching Hard Swift 43 Multiply Strings Medium Swift 42 Trapping Rain Water Hard

41 First Missing Positive Hard Swift 40 Combination Sum II Medium Swift 39 Combination Sum Medium Swift 38 Count and Say Easy Swift 37 Sudoku Solver Hard Swift 36 Valid Sudoku Easy Swift 35 Search Insert Position Medium Swift 34 Search for a Range Medium Swift 33 Search in Rotated Sorted Array Hard Swift 32 Longest Valid Parentheses Hard Swift 31 Next Permutation Medium

30 Substring with Concatenation of All Words Hard

29 Divide Two Integers Medium Swift 28 Implement strStr() Easy Swfit 27 Remove Element Easy Swift 26 Remove Duplicates from Sorted Array Easy

25 Reverse Nodes in k-Group Hard Swift 24 Swap Nodes in Pairs Easy Swift 23 Merge k Sorted Lists Hard Swift 22 Generate Parentheses Medium Swift 21 Merge Two Sorted Lists Easy Swift 20 Valid Parentheses Easy Swift 19 Remove Nth Node From End of List Easy Swift 18 4Sum Medium Swift 17 Letter Combinations of a Phone Number Medium Swift 16 3Sum Closest Medium Swift 15 3Sum Medium Swift 14 Longest Common Prefix Easy Swift 13 Roman to Integer Easy Swift 12 Integer to Roman Medium Swift 11 Container With Most Water Medium

10 Regular Expression Matching Hard Swift 9 Palindrome Number Easy Swift 8 String to Integer (atoi) Easy Swift 7 Reverse Integer Easy Swift 6 ZigZag Conversion Easy Swift 5 Longest Palindromic Substring Medium Swift 4 Median of Two Sorted Arrays Hard Swift 3 Longest Substring Without Repeating Characters Medium Swift 2 Add Two Numbers Medium Swift 1 Two Sum Easy