Think in patterns.
Solve like it’s the interview.

hand-picked DSA problems in C#, Java, Python, C++ and JavaScript. Run your code, climb the leaderboard and keep your streak alive.

ArraysO(n²)Running

Compare neighbours, swap when out of order.

TreesDFSO(n)

Visit order:

GraphsQueueO(V+E)

Level order:

Dynamic ProgrammingO(mn)

dp[i][j] = best length for the first i and j characters.

Browse by pattern

Master the idea once, solve the whole family.

Arrays Strings Linked List Trees Graphs DP Recursion Sorting Searching Hashing Stack Queue

#	Title	Acceptance	Difficulty
1	DFS Traversal Graph · DFS · Traversal	85.64%	Easy
2	Remove Duplicates From A String String · Stack	61.68%	Easy
3	Binary Tree Post Order Traversal Tree · Recursion · Traversal	79.59%	Easy
4	Find Maximum in BST Tree · Traversal · Binary Tree	85.54%	Easy
5	Find Minimum in BST Tree · Traversal · Binary Tree	85.18%	Easy
6	Count Non-Leaf Nodes In Binary Tree Tree · Traversal · Binary Tree	60.48%	Easy
7	Search / Insert into BST Tree · Traversal · Binary Tree	89.54%	Easy
8	Binary Tree Level Order Traversal Tree · Recursion · Traversal	79.68%	Easy
9	Binary Tree Inorder Traversal Recursion · Trees · Traversal	75.68%	Easy
10	Binary Tree Preorder Traversal Tree · Recursion · Binary Tree	79.85%	Easy
11	Smallest window of 0, 1 and 2 String	50.00%	Easy
12	Roman Number to Integer String	43.21%	Easy
13	Longest Common Prefix Array · String	44.20%	Easy
14	Bitonic Point Searching Algorithm	58.67%	Easy
15	Reverse Words In A String String	47.80%	Easy
16	Winner of an election String · Hashing	53.75%	Easy
17	Find Kth Rotation Array · Stack · Searching Algorithm	23.16%	Easy

Three steps, repeated every day.

1
Pick a pattern
Start from an idea such as two pointers or BFS, then move through easy, medium and hard.
2
Code and run
Write in your language, run on sample cases and submit against every hidden test.
3
Climb the board
Every solve earns points. Keep a daily streak and see where you stand this month.