Stack – Interview Questions and Practice Problems

A stack is a linear Last-In-Last-Out (LIFO) data structure which means that the last element added to the stack will be the first one to be removed. Therefore, once a new element is added to the stack, all elements that were added after it has to be removed before the new element can be removed.

 
In this post, we have listed out commonly asked interview questions that use stack data structure:

1. Stack implementation using an array – C, C++, Java, PythonBeginner
2. Stack Implementation using a Linked ListBeginner
3. Implement a stack using the queue data structureMedium
4. Implement a queue using the stack data structureMedium
5. Design a stack that returns the minimum element in constant timeHard
6. Design a stack that returns a minimum element without using an auxiliary stackHard
7. Implement two stacks in a single arrayEasy
8. Recursive solution to sort a stackHard
9. Reverse a stack using recursionHard
10. Reverse a string using a stack data structureEasy
11. Check if an expression is balanced or notEasy
12. Find duplicate parenthesis in an expressionMedium
13. Evaluate a postfix expressionEasy
14. Decode a given sequence to construct a minimum number without repeated digitsHard
15. Merging Overlapping IntervalsMedium
16. Convert an infix expression into a postfix expressionMedium
17. Find the next greater element for every element in a circular arrayHard
18. Find the next greater element for every array elementMedium
19. Find the previous smaller element for each array elementMedium
20. Reverse an array in C++Easy
21. Longest Increasing Subsequence ProblemHard
22. Find all elements in an array that are greater than all elements to their rightEasy
23. Iterative Implementation of QuicksortMedium
24. Find all binary strings that can be formed from a wildcard patternMedium
25. Find the length of the longest balanced parenthesis in a stringHard
26. Reverse text without reversing individual wordsMedium
27. Reverse a string without using recursionEasy
28. Inorder Tree TraversalMedium
29. Preorder Tree TraversalMedium
30. Postorder Tree TraversalMedium
31. Check if two binary trees are identical or notEasy
32. Find ancestors of a given node in a binary treeMedium
33. Iteratively print the leaf to root path for every leaf node in a binary treeMedium
34. Find preorder traversal of a binary tree from its inorder and postorder sequenceHard
35. Construction of an expression treeEasy
36. Print complete Binary Search Tree (BST) in increasing orderEasy
37. Depth First Search (DFS)Medium
38. Check whether the leaf traversal of given binary trees is the same or notHard
39. Reverse level order traversal of a binary treeEasy
40. Invert Binary TreeEasy
41. Invert alternate levels of a perfect binary treeHard
42. Depth-First Search (DFS) vs Breadth-First Search (BFS)Beginner