61+ Coding Interview Questions (With Sample Answers)

Technical interviews can be challenging, but strong preparation can make all the difference. Whether you’re applying for a software engineering, data science, or full-stack development role, coding interviews test your problem-solving skills, algorithmic thinking, and coding efficiency.

To help you succeed, hiring managers ask coding interview questions that range from basic programming concepts to advanced data structures and algorithms. This guide covers 30 commonly asked questions, sample answers, and expert tips so you can ace your next coding interview!

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What is a Coding Interview?

A coding interview is a technical assessment where interviewers evaluate your programming skills, problem-solving abilities, and understanding of key computer science concepts. The goal is to see how efficiently you can write and optimize code while thinking critically.

During a coding interview, you may be tested on:

• Data structures (arrays, linked lists, trees, graphs, etc.)
• Algorithms (sorting, searching, recursion, dynamic programming, etc.)
• Time and space complexity (Big-O analysis)
• System design and object-oriented programming
• Debugging and code optimization techniques

Mastering these topics will help you stand out in competitive technical interviews.

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30 Coding Interview Questions (Organized for Easy Practice!)

Here are 30 must-know coding interview questions, categorized by topic:

Data Structures

1. How do you reverse a linked list?
2. What is the difference between a stack and a queue?
3. How do you check if a binary tree is balanced?
4. What is the best way to detect a loop in a linked list?
5. How do you merge two sorted arrays?

Algorithms & Problem-Solving

6. Can you implement a binary search algorithm?
7. How does quicksort work, and can you write its implementation?
8. Explain depth-first search (DFS) and breadth-first search (BFS).
9. How do you find the shortest path in a graph?
10. What is dynamic programming, and can you give an example of its application?

String Manipulation

11. How do you determine if a string is a palindrome?
12. Write a function to count the number of vowels in a given string.
13. How can you remove duplicate characters from a string?
14. Implement a function to check if two strings are anagrams.
15. How do you reverse the words in a sentence without reversing the characters?

Sorting & Searching

16. What are the differences between merge sort, quicksort, and heapsort?
17. How do you find the median of two sorted arrays?
18. Can you implement a linear search and a binary search algorithm?
19. How do you sort an array with only 0s, 1s, and 2s?
20. How does radix sort work, and in what scenarios should it be used?

Recursion & Backtracking

21. Write a function to generate all possible subsets of a set.
22. How do you solve the N-Queens problem using backtracking?
23. Implement a function for finding all permutations of a string.
24. What are the base cases in a recursive Fibonacci sequence function?
25. How do you avoid infinite recursion in recursive algorithms?

System Design & Optimization

26. How would you design a URL shortener like Bit.ly?
27. What are the key considerations when designing a scalable database?
28. How would you efficiently implement an autocomplete feature?
29. Explain caching and how it improves system performance.
30. How do you handle millions of requests per second in a web application?

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Also Read- Change Management Interview Questions

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Sample Answers for Coding Interview Questions

Here are five commonly asked coding interview questions with sample answers to help you structure your responses:

1. How do you reverse a linked list?

📌 Sample Answer (Python):

python

CopyEdit

class ListNode:

    def __init__(self, val=0, next=None):

        self.val = val

        self.next = next

def reverse_linked_list(head):

    prev = None

    current = head

    while current:

        next_node = current.next

        current.next = prev

        prev = current

        current = next_node

    return prev

This function reverses a linked list by iterating through it while adjusting pointers.

2. How do you determine if a string is a palindrome?

📌 Sample Answer (Python):

python

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def is_palindrome(s):

    return s == s[::-1]

This function checks if a string reads the same forward and backward using Python slicing.

3. How do you find the shortest path in a graph?

📌 Sample Answer (Dijkstra’s Algorithm – Python):

python

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import heapq

def dijkstra(graph, start):

    heap = [(0, start)]

    shortest_paths = {start: 0}

    while heap:

        (cost, node) = heapq.heappop(heap)

        for neighbor, weight in graph.get(node, []):

            new_cost = cost + weight

            if new_cost < shortest_paths.get(neighbor, float(‘inf’)):

                shortest_paths[neighbor] = new_cost

                heapq.heappush(heap, (new_cost, neighbor))

    return shortest_paths

This implementation finds the shortest path from a starting node using Dijkstra’s algorithm.

4. How do you implement a binary search algorithm?

📌 Sample Answer (Python):

python

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def binary_search(arr, target):

    left, right = 0, len(arr) – 1

    while left <= right:

        mid = (left + right) // 2

        if arr[mid] == target:

            return mid

        elif arr[mid] < target:

            left = mid + 1

        else:

            right = mid – 1

    return -1

This function searches for a target element in a sorted array using the binary search technique.

5. How do you merge two sorted arrays?

📌 Sample Answer (Python):

python

CopyEdit

def merge_sorted_arrays(arr1, arr2):

    return sorted(arr1 + arr2)

This simple approach merges two sorted arrays and sorts them.

📌 Now, prepare answers for the remaining questions using this structured approach!

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Tips to Answer Coding Interview Questions

You Should Explain Your Thought Process Clearly

Before coding, walk through your approach step by step so the interviewer understands your reasoning.

You Should Optimize Your Code

After writing a solution, discuss how you can improve its time and space complexity.

You Should Handle Edge Cases

Always consider empty inputs, very large inputs, or invalid cases in your solutions.

You Should Write Clean & Readable Code

Use proper variable names, indentation, and comments to keep your code easy to follow.

You Should Practice Live Coding

Many interviews require solving problems in real time, so practice coding on a whiteboard or online platforms.

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Conclusion: Be Ready to Solve Any Coding Challenge!

Mastering coding interview questions is about understanding fundamental concepts, optimizing solutions, and explaining your approach clearly. With practice, structured thinking, and strong problem-solving skills, you’ll be fully prepared to impress hiring managers in your next technical interview.

Now, grab your notebook, start practicing, and get ready to land that dream tech job! 🚀

💬 Which coding interview question do you find the hardest? Drop it in the comments!