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πŸ“ Python / C++ 11 Solutions of LeetCode Questions

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The number of LeetCode questions is increasing every week. 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: "πŸ“–" means you need to subscribe to LeetCode premium membership for the access to premium questions.)

Algorithms

Database

Shell

Bit Manipulation

# Title Solution Time Space Difficulty Tag Note
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 πŸ“–
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

Array

# Title Solution Time Space Difficulty Tag Note
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 πŸ“–
158 Read N Characters Given Read4 II - Call multiple times C++ Python O(n) O(1) Hard πŸ“–
163 Missing Ranges C++ Python O(n) O(1) Medium πŸ“–
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++ Python O(n) O(1) Medium Binary Search
215 Kth Largest Element in an Array C++ Python O(n) ~ O(n^2) O(1) Medium EPI
228 Summary Ranges C++ Python 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 πŸ“–
245 Shortest Word Distance III C++ Python O(n) O(1) Medium πŸ“–
251 Flatten 2D Vector C++ Python O(1) O(1) Medium πŸ“–
277 Find the Celebrity C++ Python O(n) O(1) Medium πŸ“–, 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 πŸ“–
296 Best Meeting Point C++ Python O(m * n) O(m + n) Hard πŸ“–
311 Sparse Matrix Multiplication C++ Python O(m * n * l) O(m * l) Medium πŸ“–
334 Increasing Triplet Subsequence C++ Python O(n) O(1) Medium
370 Range Addition C++ Python O(k + n) O(1) Medium πŸ“–
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 πŸ“–
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

String

# Title Solution Time Space Difficulty Tag Note
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 πŸ“–
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 πŸ“–
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 πŸ“–
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 πŸ“–
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
556 Next Greater Element III C++ Python O(1) O(1) Medium
557 Reverse Words in a String III C++ Python O(n) O(1) Easy

Linked List

# Title Solution Time Space Difficulty Tag Note
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 πŸ“– Two Pointers
445 Add Two Numbers II C++ Python O(m + n) O(m + n) Medium

Stack

# Title Solution Time Space Difficulty Tag Note
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 πŸ“–
272 Closest Binary Search Tree Value II C++ Python O(h + k) O(h) Hard πŸ“–
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 πŸ“– 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 πŸ“–
456 132 Pattern C++ Python O(n) O(n) Medium

Queue

# Title Solution Time Space Difficulty Tag Note
239 Sliding Window Maximum C++ Python O(n) O(k) Hard EPI, LintCode
281 Zigzag Iterator C++ Python O(n) O(k) Medium πŸ“–
346 Moving Average from Data Stream C++ Python O(1) O(w) Easy πŸ“–

Heap

# Title Solution Time Space Difficulty Tag Note
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 πŸ“– 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

Tree

# Title Solution Time Space Difficulty Tag Note
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 πŸ“– DFS, Segment Tree, BIT
315 Count of Smaller Numbers After Self C++ Python O(nlogn) O(n) Hard LintCode BST, BIT, Divide and Conquer

Hash Table

# Title Solution Time Space Difficulty Tag Note
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 πŸ“–
170 Two Sum III - Data structure design C++ Python O(n) O(n) Easy πŸ“–
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 πŸ“–
246 Strobogrammatic Number C++ Python O(n) O(1) Easy πŸ“–
249 Group Shifted Strings C++ Python O(nlogn) O(n) Easy πŸ“–
266 Palindrome Permutation C++ Python O(n) O(1) Easy πŸ“–
288 Unique Word Abbreviation C++ Python ctor: O(n), lookup: O(1) O(k) Easy πŸ“–
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, πŸ“– Union Find
314 Binary Tree Vertical Order Traversal C++ Python O(n) O(n) Medium πŸ“– BFS
323 Number of Connected Components in an Undirected Graph C++ Python O(n) O(n) Medium πŸ“– Union Find
325 Maximum Size Subarray Sum Equals k C++ Python O(n) O(n) Medium πŸ“–
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 πŸ“–
356 Line Reflection C++ Python O(n) O(n) Medium πŸ“– 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
554 Brick Wall C++ Python O(n) O(m) Medium

Data Structure

# Title Solution Time Space Difficulty Tag Note
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

Math

# Title Solution Time Space Difficulty Tag Note
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 πŸ“–
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 πŸ“–

Sort

# Title Solution Time Space Difficulty Tag Note
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 πŸ“–
253 Meeting Rooms II C++ Python O(nlogn) O(n) Medium πŸ“–
274 H-Index C++ Python O(n) O(n) Medium Counting Sort
280 Wiggle Sort C++ Python O(n) O(1) Medium πŸ“–
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

Two Pointers

# Title Solution Time Space Difficulty Tag Note
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 πŸ“–, 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 πŸ“–
457 Circular Array Loop C++ Python O(n) O(1) Medium

Recursion

# Title Solution Time Space Difficulty Tag Note
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 πŸ“–
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 πŸ“–
327 Count of Range Sum C++ Python O(nlogn) O(n) Hard
333 Largest BST Subtree C++ Python O(n) O(h) Medium πŸ“–
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) O(h) Easy
549 Binary Tree Longest Consecutive Sequence II C++ Python O(n) O(h) Medium πŸ“–

Binary Search

# Title Solution Time Space Difficulty Tag Note
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 πŸ“–
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

Binary Search Tree

# Title Solution Time Space Difficulty Tag Note
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 πŸ“–
285 Inorder Successor in BST C++ Python O(h) O(1) Medium πŸ“–
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

Breadth-First Search

# Title Solution Time Space Difficulty Tag Note
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 πŸ“–
269 Alien Dictionary C++ Python O(n) O(1) Hard πŸ“– Topological Sort, BFS, DFS
286 Walls and Gates C++ Python O(m * n) O(g) Medium πŸ“–
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 πŸ“–
433 Minimum Genetic Mutation C++ Python O(n * b) O(b) Medium
444 Sequence Reconstruction C++ Python O(n * s) O(n) Medium πŸ“– Topological Sort

Depth-First Search

# Title Solution Time Space Difficulty Tag Note
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 πŸ“–
250 Count Univalue Subtrees C++ Python O(n) O(h) Medium πŸ“–
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 πŸ“–
364 Nested List Weight Sum II C++ Python O(n) O(h) Medium πŸ“–
366 Find Leaves of Binary Tree C++ Python O(n) O(h) Medium πŸ“–
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

Backtracking

# Title Solution Time Space Difficulty Tag Note
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 πŸ“–
267 Palindrome Permutation II C++ Python O(n * n!) O(n) Medium πŸ“–
291 Word Pattern II C++ Python O(n * C(n - 1, c - 1)) O(n + c) Hard πŸ“–
294 Flip Game II C++ Python O(n + c^2) O(c) Medium πŸ“– DP, Hash
320 Generalized Abbreviation C++ Python O(n * 2^n) O(n) Medium πŸ“–
425 Word Squares C++ Python O(n^2 * n!) O(n^2) Hard πŸ“–

Dynamic Programming

# Title Solution Time Space Difficulty Tag Note
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 πŸ“–
265 Paint House II C++ Python O(n * k) O(k) Hard πŸ“–
276 Paint Fence C++ Python O(n) O(1) Easy πŸ“–
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 πŸ“– 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 πŸ“–
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 πŸ“–
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 πŸ“–
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 πŸ“–
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

Greedy

# Title Solution Time Space Difficulty Tag Note
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

Design

# Title Solution Time Space Difficulty Tag Note
284 Peeking Iterator C++ Python O(1) O(1) Medium
348 Design Tic-Tac-Toe C++ Python O(1) O(n^2) Medium πŸ“–
353 Design Snake Game C++ Python O(1) O(s) Medium πŸ“– 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 πŸ“– Deque
362 Design Hit Counter C++ Python O(1), amortized O(k) Medium πŸ“– Deque
379 Design Phone Directory C++ Python O(1) O(n) Medium πŸ“–
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

SQL

# Title Solution Time Space Difficulty Tag Note
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

Shell Script

# Title Solution Time Space Difficulty Tag Note
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

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