Data Structure and Algorithm Coding Interview Questions Quiz

Challenge your understanding of core data structures and fundamental algorithms with practical coding interview questions designed for beginners and intermediate learners.

1. Reversing an Array

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

   1. Insert all elements into a stack and pop them
   2. Create a new array and copy elements in reverse order
   3. Swap elements from both ends towards the center
   4. Sort the array in descending order

   Explanation: Swapping elements from both ends of the array moving towards the center efficiently reverses the array in place and uses no extra space. Inserting into a stack or copying into a new array uses additional memory, which is not ideal. Sorting does not guarantee a reversed order but arranges elements by value.

2. Finding Duplicates in Arrays

   What is a simple method to check if an array contains duplicate elements?

   1. Calculate the average of all elements
   2. Double each element in the array
   3. Use a hash set to store seen elements while traversing
   4. Sort the array and remove all odd elements

   Explanation: Using a hash set allows efficient detection of duplicates by checking for existing entries as you traverse the array. Calculating the average or doubling elements does not identify duplicates. Sorting and removing odds is unrelated to duplicate detection.

3. Detecting Cycles in Linked Lists

   Which technique can be used to detect if a singly linked list has a cycle?

   1. Delete the tail node repeatedly
   2. Use two pointers moving at different speeds
   3. Convert the list into an array
   4. Sort the list elements

   Explanation: Using the two-pointer (slow and fast) technique efficiently identifies cycles in a linked list. Sorting or converting to an array does not solve the problem, and deleting tail nodes will eventually destroy the list without detecting cycles.

4. Balanced Parentheses with Stacks

   How can a stack be used to check if a string of parentheses, brackets, and braces is balanced?

   1. Push open symbols onto the stack and pop for each matching close symbol
   2. Sort all symbols alphabetically
   3. Replace all brackets with spaces
   4. Count the total number of all brackets

   Explanation: A stack keeps track of opening symbols, and each closing symbol must match and be popped accordingly. Sorting or counting does not consider the order and type of brackets, and replacing symbols ignores their balance.

5. Binary Search Trees: Traversal Methods

   Which traversal of a Binary Search Tree (BST) yields its elements in sorted (ascending) order?

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

   Explanation: In-order traversal visits the left subtree, node, then right subtree, giving a sorted sequence in BSTs. Pre-order, post-order, and level-order traverse nodes in different sequences that do not guarantee sorted order.