Practice problems across 75+ categories
Practice problems frequently asked at Stack • 172 problems | 23 Easy | 97 Medium | 51 Hard
| # | Problem | Difficulty | Topics |
|---|---|---|---|
| 16 | Binary Tree Inorder Traversal | Easy | StackTreeDepth-First Search |
| 17 | Binary Tree Postorder Traversal | Easy | StackTreeDepth-First Search |
| 18 | Binary Tree Preorder Traversal | Easy | StackTreeDepth-First Search |
| 19 | Brace Expansion | Unknown | StringBacktrackingStack |
| 20 | Brace Expansion II | Hard | Hash TableStringBacktracking |
| 21 | Build an Array With Stack Operations | Medium | ArrayStackSimulation |
| 22 | Build Binary Expression Tree From Infix Expression | Hard | StringStackTree |
| 23 | Buildings With an Ocean View | Medium | ArrayStackMonotonic Stack |
| 24 | Car Fleet | Medium | ArrayStackSorting |
| 25 | Car Fleet II | Hard | ArrayMathStack |
| 26 | Check if a Parentheses String Can Be Valid | Medium | StringStackGreedy |
| 27 | Check If Word Is Valid After Substitutions | Medium | StringStack |
| 28 | Clear Digits | Easy | StringStackSimulation |
| 29 | Closest Binary Search Tree Value II | Hard | Two PointersStackTree |
| 30 | Clumsy Factorial | Medium | MathStackSimulation |
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