Top 20 Most Asked Coding Questions in Interviews: A Complete Guide

Coding interviews can be daunting, especially when you’re unsure what to expect. In this guide, we’ll explore the top 20 most asked coding questions in interviews, complete with explanations and code examples…

Table of Contents

1. Reverse a String

Description: Write a function to reverse a string in-place.
Why it’s asked: Tests your understanding of basic string manipulation and algorithms.
Example: Input: "hello", Output: "olleh".

2. Find the Missing Number

Description: Given an array containing n distinct numbers taken from 0, 1, 2, ..., n, find the missing number.
Why it’s asked: Evaluates your ability to work with arrays and mathematical reasoning.
Example: Input: [3, 0, 1], Output: 2.

3. Check for Palindrome

Description: Determine if a given string or number is a palindrome.
Why it’s asked: Tests your understanding of string/array traversal and comparison.
Example: Input: "madam", Output: True.

4. Two Sum Problem

Description: Given an array of integers and a target sum, find two numbers that add up to the target.
Why it’s asked: Assesses your knowledge of hash maps and efficient searching.
Example: Input: [2, 7, 11, 15], Target: 9, Output: [2, 7].

5. Fibonacci Sequence

Description: Generate the Fibonacci sequence up to n terms or find the nth Fibonacci number.
Why it’s asked: Tests your understanding of recursion and dynamic programming.
Example: Input: n = 5, Output: 0, 1, 1, 2, 3.

6. Linked List Cycle Detection

Description: Determine if a linked list has a cycle.
Why it’s asked: Evaluates your knowledge of linked lists and two-pointer techniques.
Example: Input: Linked list with a cycle, Output: True.

7. Merge Two Sorted Arrays

Description: Merge two sorted arrays into one sorted array.
Why it’s asked: Tests your ability to work with arrays and sorting algorithms.
Example: Input: [1, 3, 5] and [2, 4, 6], Output: [1, 2, 3, 4, 5, 6].

8. Binary Search

Description: Implement the binary search algorithm to find an element in a sorted array.
Why it’s asked: Assesses your understanding of divide-and-conquer algorithms.
Example: Input: [1, 2, 3, 4, 5], Target: 3, Output: 2 (index).

9. Reverse a Linked List

Description: Reverse a singly linked list.
Why it’s asked: Tests your knowledge of linked list manipulation.
Example: Input: 1 -> 2 -> 3, Output: 3 -> 2 -> 1.

10. Find the Longest Substring Without Repeating Characters

Description: Given a string, find the length of the longest substring without repeating characters.
Why it’s asked: Evaluates your ability to work with strings and sliding window techniques.
Example: Input: "abcabcbb", Output: 3 (for "abc").

11. Implement a Stack Using Arrays/Linked Lists

Description: Write code to implement a stack with push, pop, and peek operations.
Why it’s asked: Tests your understanding of basic data structures.
Example: Input: Push 1, Push 2, Pop, Output: 2.

12. Check for Balanced Parentheses

Description: Determine if a string of parentheses is balanced.
Why it’s asked: Assesses your knowledge of stacks and string parsing.
Example: Input: "({[]})", Output: True.

13. Find the Maximum Subarray Sum (Kadane’s Algorithm)

Description: Find the contiguous subarray with the largest sum.
Why it’s asked: Tests your understanding of dynamic programming.
Example: Input: [-2, 1, -3, 4, -1, 2, 1, -5, 4], Output: 6 (for [4, -1, 2, 1]).

14. Implement a Queue Using Stacks

Description: Implement a queue using two stacks.
Why it’s asked: Evaluates your ability to manipulate data structures.
Example: Input: Enqueue 1, Enqueue 2, Dequeue, Output: 1.

15. Find the Kth Largest Element in an Array

Description: Given an array, find the kth largest element.
Why it’s asked: Tests your knowledge of sorting and partitioning algorithms.
Example: Input: [3, 2, 1, 5, 6, 4], k = 2, Output: 5.

16. Detect Duplicates in an Array

Description: Check if an array contains duplicates.
Why it’s asked: Assesses your understanding of hash sets and arrays.
Example: Input: [1, 2, 3, 1], Output: True.

17. Rotate an Array

Description: Rotate an array to the right by k steps.
Why it’s asked: Tests your ability to manipulate arrays efficiently.
Example: Input: [1, 2, 3, 4, 5], k = 2, Output: [4, 5, 1, 2, 3].

18. Implement a Binary Tree Traversal (Inorder, Preorder, Postorder)

Description: Write code to traverse a binary tree in different orders.
Why it’s asked: Evaluates your understanding of tree data structures and recursion.
Example: Input: Binary tree, Output: Traversal order.

19. Find the Intersection of Two Linked Lists

Description: Given two linked lists, find the node at which they intersect.
Why it’s asked: Tests your knowledge of linked lists and pointer manipulation.
Example: Input: Two intersecting linked lists, Output: Intersection node.

20. Implement a Hash Table

Description: Write code to implement a hash table with insert, delete, and search operations.
Why it’s asked: Assesses your understanding of hashing and data structures.
Example: Input: Insert ("key", "value"), Search "key", Output: "value".

FAQs

1. How do I prepare for coding interviews?

Practice regularly on platforms like LeetCode, HackerRank, and CodeSignal.
Focus on understanding data structures (arrays, linked lists, trees, etc.) and algorithms (sorting, searching, dynamic programming).

2. What languages are best for coding interviews?

Python, Java, and C++ are popular choices due to their extensive libraries and readability.

3. How important is time complexity in coding interviews?

Extremely important! Interviewers often look for optimized solutions with efficient time and space complexity.

4. Should I memorize solutions?

No, focus on understanding the underlying concepts and patterns. Memorization won’t help with new problems.

Conclusions

Preparing for coding interviews requires practice and a solid understanding of data structures and algorithms. By mastering these top 20 coding questions, you’ll be well-equipped to tackle most technical interviews. Remember, the key is to think aloud, write clean code, and optimize for efficiency.

Good luck with your interviews! If you found this post helpful, don’t forget to share it with your friends and colleagues. Happy coding! 🚀