Top Data Structures Interview Questions

Data Structures Interview Questions

Data structures are the foundation of coding interviews. Here are the most important ones to master.

Must-Know Data Structures

Structure	Use case
Array	Indexed data
Hash Map	Fast lookups O(1)
Linked List	Dynamic insertion
Stack	LIFO (undo)
Queue	FIFO (scheduling)
Tree	Hierarchical data
Graph	Networks

Common Questions

• Reverse a linked list.
• Detect a cycle in a linked list (Floyd's algorithm).
• Implement a stack/queue.
• Find duplicates using a hash set.
• Binary tree traversal (in/pre/post-order).
• BFS vs DFS on a graph.

Time Complexity Cheat Sheet

Operation	Array	Hash Map
Access	O(1)	O(1)
Search	O(n)	O(1)
Insert	O(n)	O(1)

FAQs

Which is most important?

Hash maps and arrays appear in most problems. More in our interview prep guides.

How do I practice?

Solve problems on LeetCode grouped by data structure.