Data Structure and Algorithm Coding Interview Questions Quiz

Explore essential beginner and intermediate coding interview questions on data structures and algorithms, including arrays, linked lists, stacks, queues, and trees.

1. Reversing an Array

   Which approach reverses an array in place without using extra space?

   1. Swap elements from ends moving toward the center
   2. Create a new reversed array and copy it
   3. Replace all elements with zero
   4. Sort the array in descending order

   Explanation: Swapping elements from the ends moving inward reverses the array in place, using no extra space. Creating a new array does not work in place. Sorting produces a different result, not a reversed order. Replacing with zero removes all information from the array.

2. Finding Duplicates in an Array

   What is an efficient method to check if an array contains any duplicate elements?

   1. Reverse the array and compare to original
   2. Use a hash set to track seen elements
   3. Sort the array and remove all even numbers
   4. Sum all elements and divide by the length

   Explanation: A hash set allows quick checks for repeated elements, providing efficient detection of duplicates. Summing elements or reversing does not identify duplicates. Sorting and removing even numbers unrelatedly reduces the array and may not help in duplicate detection.

3. Linked List Cycle Detection

   Which algorithm efficiently checks if a singly linked list contains a cycle?

   1. Summing node values
   2. Recursive depth-first traversal
   3. Floyd's Tortoise and Hare
   4. Counting number of nodes

   Explanation: Floyd's Tortoise and Hare uses two pointers moving at different speeds to detect cycles efficiently. Recursive traversal risks infinite loops if cycles exist. Counting nodes or summing values cannot reliably detect cycles.

4. Balancing Parentheses Using Stacks

   How can a stack be used to check if a string of parentheses is balanced?

   1. Sum ASCII values of all parentheses
   2. Reverse the string and check if it matches the original
   3. Push opening and pop on closing, ensuring stack is empty at end
   4. Count all opening parentheses only

   Explanation: A stack can track open parentheses and verify matches when closing ones appear, with emptiness indicating balance. Counting open parentheses ignores order. Reversing the string or summing ASCII values does not ensure correct pairing.

5. Binary Search Tree Traversals

   Which traversal of a binary search tree visits all nodes in ascending order of value?

   1. In-order traversal
   2. Pre-order traversal
   3. Level-order traversal
   4. Post-order traversal

   Explanation: In-order traversal visits BST nodes in ascending order by visiting left subtree, then node, then right subtree. Pre-order and post-order visit nodes in different orders. Level-order uses breadth-first logic without guaranteeing numerical order.