DSA

50 essential problems for coding interviews — with beginner-friendly explanations and solutions in Python, Java, and C++.

All50 Arrays & Two Pointers4 Strings & Sliding Window5 HashMap3 Linked List5 Binary Search3 Stack4 Trees7 Graphs4 Dynamic Programming6 Backtracking3 Intervals3 Mixed Practice3
Showing 50 of 50 problems
# Title Topic Difficulty▲
1. Two Sum HashMap easy
2. Longest Substring Without Repeating Characters Strings & Sliding Window medium
3. Container With Most Water Arrays & Two Pointers medium
4. Remove Nth Node From End of List Linked List medium
5. Valid Parentheses Stack easy
6. Merge Two Sorted Lists Linked List easy
7. Merge K Sorted Lists Linked List hard
8. Search in Rotated Sorted Array Binary Search medium
9. Combination Sum Backtracking medium
10. Permutations Backtracking medium
11. Group Anagrams HashMap medium
12. Spiral Matrix Mixed Practice medium
13. Merge Intervals Intervals medium
14. Insert Interval Intervals medium
15. Unique Paths Dynamic Programming medium
16. Climbing Stairs Dynamic Programming easy
17. Minimum Window Substring Strings & Sliding Window hard
18. Subsets Backtracking medium
19. Decode Ways Mixed Practice medium
20. Validate Binary Search Tree Trees medium
21. Same Tree Trees easy
22. Binary Tree Level Order Traversal Trees medium
23. Maximum Depth of Binary Tree Trees easy
24. Construct Binary Tree from Preorder and Inorder Traversal Trees medium
25. Best Time to Buy and Sell Stock Arrays & Two Pointers easy
26. Valid Palindrome Strings & Sliding Window easy
27. Clone Graph Graphs medium
28. Word Break Dynamic Programming medium
29. Linked List Cycle Linked List easy
30. LRU Cache Mixed Practice medium
31. Evaluate Reverse Polish Notation Stack medium
32. Find Minimum in Rotated Sorted Array Binary Search medium
33. Min Stack Stack medium
34. House Robber Dynamic Programming medium
35. Number of Islands Graphs medium
36. Reverse Linked List Linked List easy
37. Course Schedule Graphs medium
38. Contains Duplicate Arrays & Two Pointers easy
39. Invert Binary Tree Trees easy
40. Kth Smallest Element in a BST Trees medium
41. Product of Array Except Self Arrays & Two Pointers medium
42. Valid Anagram Strings & Sliding Window easy
43. Longest Increasing Subsequence Dynamic Programming medium
44. Coin Change Dynamic Programming medium
45. Top K Frequent Elements HashMap medium
46. Pacific Atlantic Water Flow Graphs medium
47. Longest Repeating Character Replacement Strings & Sliding Window medium
48. Non-overlapping Intervals Intervals medium
49. Daily Temperatures Stack medium
50. Koko Eating Bananas Binary Search medium