Top 50 Coding Round Interview Questions 🚀

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Introduction

Coding rounds are designed to test a candidate’s problem-solving ability, logical thinking, and coding efficiency. They often include questions on strings, arrays, data structures, SQL queries, algorithms, and system design. This blog organizes the Top 50 Coding Round Interview Questions into structured sections for easy preparation.

1. Strings & Arrays

  1. Reverse a string without using built-in functions.

  2. Check if a string is a palindrome.

  3. Find the first non-repeating character in a string.

  4. Count vowels and consonants in a string.

  5. Find duplicate characters in a string.

  6. Rotate an array by k positions.

  7. Find the maximum subarray sum (Kadane’s Algorithm).

  8. Merge two sorted arrays.

  9. Find the missing number in an array.

  10. Find the intersection of two arrays.

2. Data Structures

  1. Implement a stack using arrays.

  2. Implement a queue using two stacks.

  3. Detect a cycle in a linked list.

  4. Reverse a linked list.

  5. Find the middle element of a linked list.

  6. Implement a min heap and max heap.

  7. Implement a binary search tree.

  8. Perform inorder, preorder, and postorder traversal.

  9. Find the height of a binary tree.

  10. Implement a graph using adjacency list.

3. SQL Queries

  1. Write a query to find the nth highest salary.

  2. Find duplicate records in a table.

  3. Retrieve employees who don’t have assigned projects.

  4. Write a query to get department-wise average salary.

  5. Use window functions to rank employees by salary.

  6. Write a query to count students enrolled in each course.

  7. Find customers who placed more than 5 orders.

  8. Write a query to get top 3 products by sales.

  9. Detect employees with the same manager.

  10. Write a query to calculate running totals.

4. Algorithms

  1. Implement binary search.

  2. Sort an array using quicksort.

  3. Sort an array using mergesort.

  4. Find the kth largest element in an array.

  5. Count the number of inversions in an array.

  6. Implement breadth-first search (BFS).

  7. Implement depth-first search (DFS).

  8. Find shortest path using Dijkstra’s algorithm.

  9. Implement dynamic programming solution for Fibonacci sequence.

  10. Solve the knapsack problem using DP.

5. System Design

  1. Design a URL shortener (like bit.ly).

  2. Implement an LRU cache.

  3. Design a rate limiter.

  4. Build a simple REST API for CRUD operations.

  5. Design a scalable chat application.

  6. Design a file storage system like Google Drive.

  7. Explain how to design a recommendation system.

  8. Design a system for handling millions of concurrent users.

  9. Explain how to design a distributed logging system.

  10. Design a microservices-based e-commerce application.

Conclusion

These 50 questions cover the breadth of coding round knowledge expected from candidates. From strings and arrays to data structures, SQL queries, algorithms, and system design, this list serves as a comprehensive guide for interview preparation. By practicing these problems and preparing solutions with efficiency in mind, you’ll be ready to tackle coding rounds confidently.

This was part of Interview Preparation With Bipin — Let’s Crack It!

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