Essential 75

The 75 most-asked coding interview problems. Work through them systematically — each one solved, explained, and connected to the pattern it tests. Use the sidebar to track your progress.

Problems Solved0/75(0%)
Sort:
1.Two SumArraysEasy
2.Best Time to Buy and Sell StockArraysEasy
3.Contains DuplicatePremium AccessEasy
4.Product of Array Except SelfPremium AccessMedium
5.Maximum SubarrayPremium AccessMedium
6.Maximum Product SubarrayPremium AccessMedium
7.Find Minimum in Rotated Sorted ArrayPremium AccessMedium
8.Search in Rotated Sorted ArrayPremium AccessMedium
9.3SumPremium AccessMedium
10.Container with Most WaterPremium AccessMedium
11.Valid AnagramPremium AccessEasy
12.Valid ParenthesesPremium AccessEasy
13.Group AnagramsPremium AccessMedium
14.Valid PalindromePremium AccessEasy
15.Longest Substring Without Repeating CharactersPremium AccessMedium
16.Longest Palindromic SubstringPremium AccessMedium
17.Palindromic SubstringsPremium AccessMedium
18.Encode and Decode StringsPremium AccessMedium
19.Minimum Window SubstringPremium AccessHard
20.Reverse Linked ListPremium AccessEasy
21.Merge Two Sorted ListsPremium AccessEasy
22.Linked List CyclePremium AccessEasy
23.Reorder ListPremium AccessMedium
24.Remove Nth Node From End of ListPremium AccessMedium
25.Merge K Sorted ListsPremium AccessHard
26.Invert Binary TreePremium AccessEasy
27.Maximum Depth of Binary TreePremium AccessEasy
28.Same TreePremium AccessEasy
29.Subtree of Another TreePremium AccessEasy
30.Lowest Common Ancestor of BSTPremium AccessMedium
31.Binary Tree Level Order TraversalPremium AccessMedium
32.Validate Binary Search TreePremium AccessMedium
33.Kth Smallest Element in a BSTPremium AccessMedium
34.Construct Binary Tree from Preorder and InorderPremium AccessMedium
35.Binary Tree Maximum Path SumPremium AccessHard
36.Serialize and Deserialize Binary TreePremium AccessHard
37.Implement Trie (Prefix Tree)Premium AccessMedium
38.Design Add and Search Words Data StructurePremium AccessMedium
39.Word Search IIPremium AccessHard
40.Top K Frequent ElementsPremium AccessMedium
41.Find Median from Data StreamPremium AccessHard
42.Combination SumPremium AccessMedium
43.Word SearchPremium AccessMedium
44.Number of IslandsPremium AccessMedium
45.Clone GraphPremium AccessMedium
46.Pacific Atlantic Water FlowPremium AccessMedium
47.Course SchedulePremium AccessMedium
48.Number of Connected ComponentsPremium AccessMedium
49.Graph Valid TreePremium AccessMedium
50.Alien DictionaryPremium AccessHard
51.Climbing StairsPremium AccessEasy
52.House RobberPremium AccessMedium
53.House Robber IIPremium AccessMedium
54.Longest Increasing SubsequencePremium AccessMedium
55.Word BreakPremium AccessMedium
56.Coin ChangePremium AccessMedium
57.Decode WaysPremium AccessMedium
58.Unique PathsPremium AccessMedium
59.Longest Common SubsequencePremium AccessMedium
60.Jump GamePremium AccessMedium
61.Merge IntervalsPremium AccessMedium
62.Insert IntervalPremium AccessMedium
63.Non-overlapping IntervalsPremium AccessMedium
64.Meeting RoomsPremium AccessEasy
65.Meeting Rooms IIPremium AccessMedium
66.Rotate ImagePremium AccessMedium
67.Spiral MatrixPremium AccessMedium
68.Set Matrix ZeroesPremium AccessMedium
69.Number of 1 BitsPremium AccessEasy
70.Counting BitsPremium AccessEasy
71.Reverse BitsPremium AccessEasy
72.Missing NumberPremium AccessEasy
73.Sum of Two IntegersPremium AccessMedium
74.Binary SearchPremium AccessEasy
75.Word SearchPremium AccessMedium