Data Structures Basics - Technical Aptitude Questions & Answers

What is the time complexity of accessing an element by index in an array?

A.O(1)

B.O(n)

C.O(log n)

D.O(n²)

Which data structure follows the LIFO (Last In First Out) principle?

A.Stack

B.Queue

C.Array

D.Linked List

What is the time complexity of inserting an element at the beginning of a singly linked list?

A.O(1)

B.O(n)

C.O(log n)

D.O(n²)

Which data structure is best suited for implementing a browser's Back button?

A.Stack

B.Queue

C.Deque

D.Heap

What is the worst-case time complexity of searching in a Binary Search Tree (BST)?

A.O(n)

B.O(log n)

C.O(1)

D.O(n log n)

In a circular queue of size N, what is the maximum number of elements it can hold?

A.N-1

B.N

C.N+1

D.N/2

Which operation is NOT supported in O(1) by a singly linked list?

A.Accessing element at index k

B.Inserting at head

C.Deleting head node

D.Checking if list is empty

What data structure is used in Breadth First Search (BFS)?

A.Queue

B.Stack

C.Heap

D.Array

What is the space complexity of storing a graph with V vertices and E edges as an adjacency matrix?

A.O(V²)

B.O(V+E)

C.O(E)

D.O(V)

Which sorting algorithm has the best average-case time complexity?

A.Merge Sort — O(n log n)

B.Bubble Sort — O(n²)

C.Selection Sort — O(n²)

D.Insertion Sort — O(n²)

What is a Min-Heap?

A.A complete binary tree where every parent ≤ its children

B.A complete binary tree where every parent ≥ its children

C.A sorted array

D.A balanced BST

What is the time complexity of enqueue and dequeue in a queue implemented with a linked list?

A.O(1) for both

B.O(n) for both

C.O(1) enqueue, O(n) dequeue

D.O(n) enqueue, O(1) dequeue

Which data structure is ideal for implementing an LRU (Least Recently Used) Cache?

A.HashMap + Doubly Linked List

B.Stack

C.Array

D.Binary Search Tree

What is the result of performing inorder traversal on a BST?

A.Elements in sorted (ascending) order

B.Elements in reverse sorted order

C.Random order

D.Level-by-level order

How many pointers does each node in a doubly linked list have?

A.2 (next and prev)

B.1 (next only)

C.3 (next, prev, data)

D.0

What is the time complexity of building a heap from an unsorted array of n elements?

A.O(n)

B.O(n log n)

C.O(log n)

D.O(n²)

What is a hash collision?

A.When two different keys produce the same hash index

B.When the hash table is full

C.When a key is not found

D.When hash function returns a negative value

Which traversal is used to delete all nodes of a binary tree?

A.Postorder

B.Preorder

C.Inorder

D.Level-order

What is the maximum number of nodes at level k of a binary tree (root at level 0)?

A.2^k

B.k²

C.2k

D.k+1

Which of the following is TRUE about dynamic arrays (like ArrayList in Java / vector in C++)?

A.Amortized O(1) insertion at end, O(n) for middle insertion

B.Always O(1) for all insertions

C.O(log n) for all insertions

D.O(n) for all operations