Top 150 best practice LeetCode’s problems sorted by difficulties4 min read

If you want to sharpen your problem-solving and coding skills, indeed Leetcode is one of the best places that help you do that. This platform empowers programmers to improve their skills through a number of coding challenges from easy to advanced. In fact, when you visit LeetCode, there are a tremendous number of problems which up to over 2000. Every problem on LeetCode is worth trying, but for the very first time, you couldn’t solve all of the problems in one or two days, it takes time, patience, effort, or even willpower. Choosing the right first ones is a good start, so in this article, I want to list the 150 most popular problems on LeetCode from easy to advanced which is based on the highest number of votes.

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Top 50 Easy Coding Problems

1. Two Sum
2. Maximum Subarray
3. Valid Parentheses
4. Best Time to Buy and Sell Stock
5. House Robber
6. Reverse Linked List
7. Single Number
8. Merge Two Sorted Lists
9. Climbing Stairs
10. Symmetric Tree
11. Intersection of Two Linked Lists
12. Reverse Integer
13. Move Zeroes
14. Path Sum III
15. Min Stack
16. Inverse Binary Tree
17. Merge Two Binary Tree
18. Majority Element
19. Palindrome Linked List
20. Find All Numbers Disappeared in an Array
21. Linked List Cycle
22. Remove Duplicates from Sorted Array
23. Diameter of Binary Tree
24. Shortest Unsorted Continuous Subarray
25. Rotate Array
26. Longest Common Prefix
27. Palindrome Number
28. Maximum Depth of Binary Tree
29. Jewels and Stones
30. Search Insert Position
31. Balanced Binary Tree
32. Convert Sorted Array to Binary Search Tree
33. Subtree of Another Tree
34. Roman to Integer
35. Convert BST to Greater Tree
36. Same Tree
37. Merge Sorted Array
38. Hamming Distance
39. Lowest Common Ancestor of a Binary Search Tree
40. Best Time to Buy and Sell Stock II  
41. Count Primes
42. Min Cost Climbing Stairs
43. Trim a Binary Search Tree 
44. Non-decreasing Array
45. Island Perimeter
46. First Unique Character in a String
47. Add Binary
48. Path Sum
49. Longest Univalue Path
50. Happy Number  

Top 50 Intermediate Coding Problems

1. Longest Substring Without Repeating Characters
2. Add Two Numbers
3. 3Sum  
4. Longest Palindromic Substring
5. Container With Most Water
6. Generate Parentheses
7. Number of Islands
8. Search in Rotated Sorted Array
9. Longest Increasing Subsequence 
10. Find the Duplicate Number
11. Product of Array Except Self
12. Word Break 
13. Merge Intervals 
14. Letter Combinations of a Phone Number
15. Subarray Sum Equals K    
16. Maximum Product Subarray
17. Permutations 
18. Combination Sum 
19. Validate Binary Search Tree
20. Jump Game
21. Kth Largest Element in an Array
22. Subsets
23. Lowest Common Ancestor of a Binary Tree
24. Coin Change
25. Course Schedule 
26. Word Search
27. Next Permutation 
28. Remove Nth Node From End of List
29. Unique Binary Search Trees
30. Construct Binary Tree from Preorder and Inorder Traversal
31. Group Anagrams
32. Find First and Last Position of Element in Sorted Array  
33. Sort Colors
34. Binary Tree Inorder Traversal
35. Copy List with Random Pointer
36. Task Scheduler 
37. Decode String
38. Search a 2D Matrix II
39. Unique Paths
40. Rotate Image 
41. Word Ladder
42. Top K Frequent Elements
43. Implement Trie (Prefix Tree)
44. Binary Tree Level Order Traversal
45. Find All Anagrams in a String    
46. Flatten Binary Tree to Linked List
47. Queue Reconstruction by Height 
48. Meeting Rooms II  
49. Sort List
50. House Robber III

Top 50 Hard Coding Problems

1. Median of Two Sorted Arrays
2. Trapping Rain Water 
3. Regular Expression Matching
4. Merge k Sorted Lists
5. Minimum Window Substring
6. Edit Distance
7. Largest Rectangle in Histogram
8. Longest Valid Parentheses
9. Longest Consecutive Sequence
10. First Missing Positive
11. Sliding Window Maximum
12. Binary Tree Maximum Path Sum
13. Serialize and Deserialize Binary Tree
14. Maximal Rectangle 
15. Remove Invalid Parentheses
16. Burst Balloons
17. Find Median from Data Stream
18. Jump Game II
19. Word Search II
20. Count of Smaller Numbers After Self
21. Reverse Nodes in k-Group
22. The Skyline Problem 
23. Best Time to Buy and Sell Stock III
24. Wildcard Matching 
25. Longest Increasing Path in a Matrix   
26. Word Ladder II
27. Word Break II
28. N-Queens    
29. Sudoku Solver
30. Binary Tree Postorder Traversal
31. Alien Dictionary 
32. Split Array Largest Sum
33. Insert Interval
34. Recover Binary Search Tree
35. Basic Calculator     
36. Best Time to Buy and Sell Stock IV
37. Interleaving String
38. Palindrome Pairs 
39. LFU Cache    
40. Remove Duplicate Letters
41. Trapping Rain Water
42. Dungeon Game
43. Expression Add Operators
44. Distinct Subsequences 
45. Smallest Range Covering Elements from K Lists   
46. Shortest Palindrome
47. Palindrome Partitioning II
48. Russian Doll Envelopes   
49. Longest Substring with at most K Distinct Characters
50. Robot Room Cleaner

Above I have listed 150 best practice LeetCode’s coding questions from easy to hard based on the number of upvotes per each question, from highest upvote numbers and gradually decrease by. And if needed, this is the repository that has solutions for most of the problems above: https://github.com/haoel/leetcode. Hope you have time to practice with some of them. Happy coding!