All 355 coding interview problems

All 355 algorithm interview problems, filterable by pattern, difficulty and status. Every problem runs in your browser with tests and AI hints. Free to start: no credit card, no install. Pro is $19.99 a month or $129 a year.

Array & Hash Table

1. Two Sum · Easy
13. Roman to Integer · Easy
14. Longest Common Prefix · Easy
27. Remove Element · Easy
36. Valid Sudoku · Medium
41. First Missing Positive · Hard
43. Multiply Strings · Medium
48. Rotate Image · Medium
49. Group Anagrams · Medium
50. Pow(x, n) · Medium
54. Spiral Matrix · Medium
66. Plus One · Easy
68. Text Justification · Hard
73. Set Matrix Zeroes · Medium
75. Sort Colors · Medium
128. Longest Consecutive Sequence · Medium
168. Excel Sheet Column Title · Easy
169. Majority Element · Easy
202. Happy Number · Easy
217. Contains Duplicate · Easy
229. Majority Element II · Medium
238. Product of Array Except Self · Medium
242. Valid Anagram · Easy
249. Group Shifted Strings · Medium
271. Encode and Decode Strings · Medium
304. Range Sum Query 2D - Immutable · Medium
325. Maximum Size Subarray Sum Equals k · Medium
347. Top K Frequent Elements · Medium
359. Logger Rate Limiter · Easy
380. Insert Delete GetRandom O(1) · Medium
560. Subarray Sum Equals K · Medium
641. Design Circular Deque · Medium
705. Design HashSet · Easy
706. Design HashMap · Easy
850. Rectangle Area II · Hard
867. Transpose Matrix · Easy
912. Sort an Array · Medium
939. Minimum Area Rectangle · Medium
963. Minimum Area Rectangle II · Medium
1071. Greatest Common Divisor of Strings · Easy
1929. Concatenation of Array · Easy
2013. Detect Squares · Medium
2534. Time Taken to Cross the Door · Hard
2807. Insert Greatest Common Divisors in Linked List · Medium
3355. Zero Array Transformation I · Medium
Count Pairs With Target Sum · Easy

Two Pointers

11. Container With Most Water · Medium
15. 3Sum · Medium
18. 4Sum · Medium
26. Remove Duplicates from Sorted Array · Easy
42. Trapping Rain Water · Hard
80. Remove Duplicates from Sorted Array II · Medium
88. Merge Sorted Array · Easy
125. Valid Palindrome · Easy
151. Reverse Words in a String · Medium
167. Two Sum II - Input Array Is Sorted · Medium
189. Rotate Array · Medium
283. Move Zeroes · Easy
344. Reverse String · Easy
532. K-diff Pairs in an Array · Medium
680. Valid Palindrome II · Easy
777. Swap Adjacent in LR String · Medium
881. Boats to Save People · Medium
986. Interval List Intersections · Medium
1768. Merge Strings Alternately · Easy
2337. Move Pieces to Obtain a String · Medium
Remove Extra Spaces · Easy
Remove Every Duplicated Value · Medium

Sliding Window

3. Longest Substring Without Repeating Characters · Medium
76. Minimum Window Substring · Hard
209. Minimum Size Subarray Sum · Medium
219. Contains Duplicate II · Easy
239. Sliding Window Maximum · Hard
340. Longest Substring with At Most K Distinct Characters · Medium
346. Moving Average from Data Stream · Easy
424. Longest Repeating Character Replacement · Medium
438. Find All Anagrams in a String · Medium
480. Sliding Window Median · Hard
567. Permutation in String · Medium
658. Find K Closest Elements · Medium
862. Shortest Subarray with Sum at Least K · Hard
1004. Max Consecutive Ones III · Medium

Binary Search

4. Median of Two Sorted Arrays · Hard
33. Search in Rotated Sorted Array · Medium
34. Find First and Last Position of Element in Sorted Array · Medium
35. Search Insert Position · Easy
69. Sqrt(x) · Easy
74. Search a 2D Matrix · Medium
81. Search in Rotated Sorted Array II · Medium
153. Find Minimum in Rotated Sorted Array · Medium
154. Find Minimum in Rotated Sorted Array II · Hard
275. H-Index II · Medium
374. Guess Number Higher or Lower · Easy
410. Split Array Largest Sum · Hard
702. Search in a Sorted Array of Unknown Size · Medium
704. Binary Search · Easy
715. Range Module · Hard
729. My Calendar I · Medium
792. Number of Matching Subsequences · Medium
875. Koko Eating Bananas · Medium
981. Time Based Key-Value Store · Medium
1011. Capacity to Ship Packages Within D Days · Medium
1095. Find in Mountain Array · Hard
1970. Last Day Where You Can Still Cross · Hard
3453. Separate Squares I · Medium
Missing Number in a Sorted Range · Easy

Linked List

2. Add Two Numbers · Medium
19. Remove Nth Node From End of List · Medium
21. Merge Two Sorted Lists · Easy
23. Merge k Sorted Lists · Hard
24. Swap Nodes in Pairs · Medium
25. Reverse Nodes in k-Group · Hard
61. Rotate List · Medium
86. Partition List · Medium
92. Reverse Linked List II · Medium
138. Copy List with Random Pointer · Medium
141. Linked List Cycle · Easy
142. Linked List Cycle II · Medium
143. Reorder List · Medium
146. LRU Cache · Medium
148. Sort List · Medium
203. Remove Linked List Elements · Easy
206. Reverse Linked List · Easy
234. Palindrome Linked List · Easy
287. Find the Duplicate Number · Medium
445. Add Two Numbers II · Medium
460. LFU Cache · Hard
622. Design Circular Queue · Medium
876. Middle of the Linked List · Easy

Stack

20. Valid Parentheses · Easy
71. Simplify Path · Medium
84. Largest Rectangle in Histogram · Hard
85. Maximal Rectangle · Hard
150. Evaluate Reverse Polish Notation · Medium
155. Min Stack · Medium
224. Basic Calculator · Hard
225. Implement Stack Using Queues · Easy
227. Basic Calculator II · Medium
232. Implement Queue using Stacks · Easy
394. Decode String · Medium
402. Remove K Digits · Medium
496. Next Greater Element I · Easy
503. Next Greater Element II · Medium
682. Baseball Game · Easy
716. Max Stack · Hard
735. Asteroid Collision · Medium
739. Daily Temperatures · Medium
770. Basic Calculator IV · Hard
772. Basic Calculator III · Hard
853. Car Fleet · Medium
856. Score of Parentheses · Medium
895. Maximum Frequency Stack · Hard
901. Online Stock Span · Medium
1047. Remove All Adjacent Duplicates In String · Easy
1249. Minimum Remove to Make Valid Parentheses · Medium
1673. Find the Most Competitive Subsequence · Medium
1944. Number of Visible People in a Queue · Hard
Remove Adjacent Runs Repeatedly · Medium

Binary Tree

94. Binary Tree Inorder Traversal · Easy
98. Validate Binary Search Tree · Medium
100. Same Tree · Easy
101. Symmetric Tree · Easy
102. Binary Tree Level Order Traversal · Medium
104. Maximum Depth of Binary Tree · Easy
105. Construct Binary Tree from Preorder and Inorder Traversal · Medium
106. Construct Binary Tree from Inorder and Postorder Traversal · Medium
110. Balanced Binary Tree · Easy
113. Path Sum II · Medium
124. Binary Tree Maximum Path Sum · Hard
129. Sum Root to Leaf Numbers · Medium
144. Binary Tree Preorder Traversal · Easy
145. Binary Tree Postorder Traversal · Easy
199. Binary Tree Right Side View · Medium
208. Implement Trie Prefix Tree · Medium
211. Design Add And Search Words Data Structure · Medium
212. Word Search II · Hard
226. Invert Binary Tree · Easy
230. Kth Smallest Element in a BST · Medium
235. Lowest Common Ancestor of a Binary Search Tree · Medium
236. Lowest Common Ancestor of a Binary Tree · Medium
250. Count Univalue Subtrees · Medium
285. Inorder Successor in BST · Medium
297. Serialize and Deserialize Binary Tree · Hard
337. House Robber III · Medium
427. Construct Quad Tree · Medium
437. Path Sum III · Medium
450. Delete Node in a BST · Medium
543. Diameter of Binary Tree · Easy
572. Subtree of Another Tree · Easy
642. Design Search Autocomplete System · Hard
701. Insert into a Binary Search Tree · Medium
1325. Delete Leaves With a Given Value · Medium
1448. Count Good Nodes In Binary Tree · Medium
1650. Lowest Common Ancestor of a Binary Tree III · Medium
2707. Extra Characters in a String · Medium

Dynamic Programming

5. Longest Palindromic Substring · Medium
10. Regular Expression Matching · Hard
45. Jump Game II · Medium
55. Jump Game · Medium
62. Unique Paths · Medium
63. Unique Paths II · Medium
64. Minimum Path Sum · Medium
70. Climbing Stairs · Easy
72. Edit Distance · Medium
91. Decode Ways · Medium
97. Interleaving String · Medium
115. Distinct Subsequences · Hard
139. Word Break · Medium
152. Maximum Product Subarray · Medium
198. House Robber · Medium
213. House Robber II · Medium
221. Maximal Square · Medium
279. Perfect Squares · Medium
300. Longest Increasing Subsequence · Medium
309. Best Time to Buy And Sell Stock With Cooldown · Medium
312. Burst Balloons · Hard
322. Coin Change · Medium
329. Longest Increasing Path In a Matrix · Hard
343. Integer Break · Medium
377. Combination Sum IV · Medium
416. Partition Equal Subset Sum · Medium
494. Target Sum · Medium
518. Coin Change II · Medium
647. Palindromic Substrings · Medium
746. Min Cost Climbing Stairs · Easy
877. Stone Game · Medium
940. Distinct Subsequences II · Hard
1049. Last Stone Weight II · Medium
1137. N-th Tribonacci Number · Easy
1140. Stone Game II · Medium
1143. Longest Common Subsequence · Medium
1406. Stone Game III · Hard

Graph

127. Word Ladder · Hard
130. Surrounded Regions · Medium
133. Clone Graph · Medium
200. Number of Islands · Medium
207. Course Schedule · Medium
210. Course Schedule II · Medium
261. Graph Valid Tree · Medium
269. Alien Dictionary · Hard
286. Walls And Gates · Medium
310. Minimum Height Trees · Medium
323. Number of Connected Components In An Undirected Graph · Medium
332. Reconstruct Itinerary · Hard
399. Evaluate Division · Medium
417. Pacific Atlantic Water Flow · Medium
444. Sequence Reconstruction · Medium
463. Island Perimeter · Easy
490. The Maze · Medium
505. The Maze II · Medium
542. 01 Matrix · Medium
684. Redundant Connection · Medium
695. Max Area of Island · Medium
721. Accounts Merge · Medium
743. Network Delay Time · Medium
752. Open The Lock · Medium
778. Swim In Rising Water · Hard
787. Cheapest Flights Within K Stops · Medium
953. Verifying An Alien Dictionary · Easy
994. Rotting Oranges · Medium
997. Find the Town Judge · Easy
1091. Shortest Path in Binary Matrix · Medium
1101. The Earliest Moment When Everyone Become Friends · Medium
1197. Minimum Knight Moves · Medium
1254. Number of Closed Islands · Medium
1462. Course Schedule IV · Medium
1489. Find Critical and Pseudo Critical Edges in Minimum Spanning Tree · Hard
1584. Min Cost to Connect All Points · Medium
1631. Path with Minimum Effort · Medium
1971. Find if Path Exists in Graph · Easy
2050. Parallel Courses III · Hard
2203. Minimum Weighted Subgraph With the Required Paths · Hard
2392. Build a Matrix With Conditions · Hard
2709. Greatest Common Divisor Traversal · Hard
2812. Find the Safest Path in a Grid · Medium

Greedy

53. Maximum Subarray · Medium
56. Merge Intervals · Medium
57. Insert Interval · Medium
121. Best Time to Buy and Sell Stock · Easy
122. Best Time to Buy and Sell Stock II · Medium
134. Gas Station · Medium
135. Candy · Hard
252. Meeting Rooms · Easy
253. Meeting Rooms II · Medium
435. Non Overlapping Intervals · Medium
452. Minimum Number of Arrows to Burst Balloons · Medium
649. Dota2 Senate · Medium
678. Valid Parenthesis String · Medium
763. Partition Labels · Medium
846. Hand of Straights · Medium
860. Lemonade Change · Easy
918. Maximum Sum Circular Subarray · Medium
978. Longest Turbulent Subarray · Medium
1851. Minimum Interval to Include Each Query · Hard
1871. Jump Game VII · Medium
1899. Merge Triplets to Form Target Triplet · Medium
2402. Meeting Rooms III · Hard

Backtracking

17. Letter Combinations of a Phone Number · Medium
22. Generate Parentheses · Medium
39. Combination Sum · Medium
40. Combination Sum II · Medium
46. Permutations · Medium
47. Permutations II · Medium
51. N Queens · Hard
52. N Queens II · Hard
77. Combinations · Medium
78. Subsets · Medium
79. Word Search · Medium
90. Subsets II · Medium
93. Restore IP Addresses · Medium
131. Palindrome Partitioning · Medium
140. Word Break II · Hard
216. Combination Sum III · Medium
351. Android Unlock Patterns · Medium
473. Matchsticks to Square · Medium
698. Partition to K Equal Sum Subsets · Medium
1863. Sum of All Subsets XOR Total · Easy

Heap

215. Kth Largest Element in an Array · Medium
295. Find Median from Data Stream · Hard
355. Design Twitter · Medium
378. Kth Smallest Element in a Sorted Matrix · Medium
502. IPO · Hard
621. Task Scheduler · Medium
630. Course Schedule III · Hard
692. Top K Frequent Words · Medium
703. Kth Largest Element in a Stream · Easy
767. Reorganize String · Medium
973. K Closest Points to Origin · Medium
1046. Last Stone Weight · Easy
1094. Car Pooling · Medium
1405. Longest Happy String · Medium
1834. Single-Threaded CPU · Medium
Smallest K Numbers · Easy
K-th Number With Factors 3, 5 and 7 · Medium

Bit Manipulation

7. Reverse Integer · Medium
29. Divide Two Integers · Medium
67. Add Binary · Easy
136. Single Number · Easy
137. Single Number II · Medium
190. Reverse Bits · Easy
191. Number of 1 Bits · Easy
201. Bitwise AND of Numbers Range · Medium
231. Power of Two · Easy
260. Single Number III · Medium
268. Missing Number · Easy
318. Maximum Product of Word Lengths · Medium
338. Counting Bits · Easy
371. Sum of Two Integers · Medium
389. Find the Difference · Easy
461. Hamming Distance · Easy
476. Number Complement · Easy
1310. XOR Queries of a Subarray · Medium
1371. Find the Longest Substring Containing Vowels in Even Counts · Medium
3133. Minimum Array End · Medium
All Characters Unique · Easy