Cracking tech interviews often comes down to one core skill: Data Structures. Whether you are a fresh graduate or an experienced professional in India, a strong grasp of data structures is crucial. Companies across the tech landscape, from startups to large corporations, consistently ask questions about how you organize and manage data efficiently. This article offers a clear guide to common Data Structures interview questions, helping you build a solid foundation and approach your next interview with confidence.
Tree Data Structure Interview Questions
- Inorder, Preorder, and Postorder Traversals (recursive & iterative)
- Level Order Traversal (BFS using Queue)
- Height/Depth of a Binary Tree
- Check if a Binary Tree is Balanced
- Diameter of a Binary Tree
- Lowest Common Ancestor (LCA) in a Binary Tree
- Convert a Sorted Array to a Balanced BST
- Check if two trees are identical
- Zigzag (Spiral) Level Order Traversal
- Boundary Traversal of a Binary Tree
- Vertical Order Traversal of a Binary Tree
- Top View / Bottom View of a Binary Tree
- Serialize and Deserialize a Binary Tree
- Construct a Binary Tree from Inorder and Preorder Traversal
- Path Sum Problems (Has path sum / Find all paths with sum)
- Mirror a Binary Tree
- Flatten a Binary Tree to a Linked List
- Validate a Binary Search Tree (BST)
- Kth Smallest/Largest Element in a BST
- Find Distance Between Two Nodes in a Binary Tree
Stacks & Queues Data Structures Interview Questions
- Implement a stack using arrays or a linked list
- Implement two stacks in one array
- Design a stack that supports getMin() in O(1) time
- Evaluate the postfix expression
- Infix to postfix conversion
- Next Greater Element
- Largest rectangle in a histogram
- Celebrity problem (using stack)
- Valid parenthesis checker
- Sort a stack using recursion
- Implement a queue using stacks
- Implement a circular queue
- LRU Cache (using Doubly Linked List + HashMap)
- First non-repeating character in a stream
- Rotten oranges (multi-source BFS using queue)
- Generate binary numbers from 1 to N using a queue
- Interleave the first half of the queue with the second half
- Reverse the first K elements of a queue
- Sliding window maximum (Monotonic queue)
- Implement a deque (double-ended queue)
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Array Data Structure Interview Questions
- Find the maximum and minimum elements in an array
- Reverse an array
- Find the “Kth” maximum and minimum element
- Move all zeros to the end of the array
- Check if an array is sorted
- Kadane’s Algorithm – Maximum subarray sum
- Find the intersection of two sorted arrays
- Sort an array of 0s, 1s, and 2s (Dutch National Flag problem)
- Find the longest subarray with a sum equal to 0
- Subarray with given sum (Sliding Window Technique)
- Find a duplicate number in an array of N+1 integers
- Merge two sorted arrays without extra space
- Minimum number of jumps to reach the end of the array
- Find the missing number from an array containing numbers from 1 to N
- Maximum product subarray
- Count inversions in an array (using Merge Sort)
- Median of two sorted arrays
- Trapping Rain Water problem
- Find all subarrays with XOR = K
- Maximum sum of i*arr[i] among all rotations of a given array
Graph Data Structure Interview Questions
- Represent a graph using an adjacency list/matrix
- Depth First Search (DFS)
- Breadth First Search (BFS)
- Detect a cycle in an undirected graph (DFS/Union-Find)
- Detect a cycle in a directed graph (DFS + Recursion Stack)
- Topological Sort (Kahn’s algorithm / DFS)
- Number of connected components in a graph
- Check if a graph is bipartite
- Clone a graph
- Shortest path in an unweighted graph (BFS)
- Dijkstra’s Algorithm for the shortest path in a weighted graph
- Bellman-Ford Algorithm
- Floyd-Warshall Algorithm (All-pairs shortest path)
- Kruskal’s Algorithm (Minimum Spanning Tree using Union-Find)
- Prim’s Algorithm (Minimum Spanning Tree using Priority Queue)
- Course Schedule problem (Cycle Detection + Topological Sort)
- Word Ladder problem (BFS)
- Alien Dictionary (Graph + Topological Sort)
- Strongly Connected Components (Kosaraju’s algorithm)
- Bridges and Articulation Points in a Graph (Tarjan’s algorithm)
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Linked List Data Structure Interview Questions
- Reverse a linked list
- Detect a cycle in a linked list (Floyd’s Cycle Detection)
- Find the middle of the linked list
- Merge two sorted linked lists
- Remove the N-th node from the end of the list
- Detect and remove a loop in a linked list
- Find the intersection point of two linked lists
- Check if a linked list is a palindrome
- Rotate a linked list by k positions
- Remove duplicates from a sorted linked list
- Delete a node without a head pointer
- Add two numbers represented by linked lists
- Clone a linked list with random pointers
- Flatten a multilevel linked list
- Sort a linked list using Merge Sort
- Reverse nodes in a k-group
- Merge K sorted linked lists
- Intersection of two sorted linked lists
- Convert a binary number in a linked list to an integer
- Swap nodes in pairs
