DSA
Master the patterns
Search the bank, then filter by difficulty, pattern, data structure, or algorithm. Each problem includes approaches, solutions, and walkthroughs.
Active·2,723
Easy·667
Medium·1,394
Hard·662
Patterns
Recognize the move
Filter the bank by pattern — each card links into the problem index.
Problem index
Browse problems
Search by title, then refine with facets. Sorted by problem ID.
Difficulty
Facets
20 of 140 matching · 2723 totalSort: id ↑
No.ProblemDifficulty
- 0020Valid ParenthesesEasy
- 0032Longest Valid ParenthesesHard
- 0042Trapping Rain WaterHard
- 0071Simplify PathMed
- 0084Largest Rectangle in HistogramHard
- 0085Maximal RectangleHard
- 0094Binary Tree Inorder TraversalEasy
- 0114Flatten Binary Tree to Linked ListMed
- 0143Reorder ListMed
- 0144Binary Tree Preorder TraversalEasy
- 0145Binary Tree Postorder TraversalEasy
- 0150Evaluate Reverse Polish NotationMed
- 0155Min StackMed
- 0173Binary Search Tree IteratorMed
- 0212Basic CalculatorHard
- 0213Implement Stack using QueuesEasy
- 0215Basic Calculator IIMed
- 0220Implement Queue using StacksEasy
- 0222Palindrome Linked ListEasy
- 0303Remove Duplicate LettersMed
Showing 20 of 140