40 Coder Interview Questions (With Sample Answers)

By Indeed Editorial Team

Published 3 January 2022

The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed's data and insights to deliver useful tips to help guide your career journey.

Preparing for an IT interview involves familiarising yourself with the technical terminology common to the industry. As a computer science graduate or programmer, there are coding, software development and programming job openings you can apply. By reviewing possible interview questions and preparing your answers, you can feel more confident during your next interview. In this article, we list 40 programming interview questions and provide sample answers to help you prepare for your next interview.

35 frequently asked coder interview questions

Coder interview questions that are frequently asked often cover data structure and algorithm-based questions and some purely logical questions. You may answer other questions outside these topics, but these give you a good idea of what kinds of questions to be ready for in a coding interview. Here are 35 questions that can help you go into your coder interviews confidently:

Sting-based programming questions

Here are 7 questions about string-based programming:

  1. How would you write a method to erase a character from a string?

  2. How would you explain the term ‘string' to a non-IT co-worker?

  3. You need to check if a string is a palindrome or not. How would you code the query?

  4. In Java, how do you convert a numeric string to int?

  5. How would you find the character with maximum occurrences in a string?

  6. Explain your process for finding the first unrepeated character of a string.

  7. Can you split a string in Java? If so, how?

Programming questions about arrays

Here are 7 questions to do with arrays:

  1. Explain your process to find the smallest and largest number in an array of 1-100?

  2. Can you explain the term ‘array' to a non-technical person?

  3. Can you reverse an array in place in Java?

  4. Define ‘integer array'.

  5. How would you find duplicate numbers in an array?

  6. Describe your process for removing duplicates from an array.

  7. Can you convert a byte array into a string?

Programming questions about linked lists

Here are 7 questions about linked lists:

  1. Explain how you'd reverse a linked list.

  2. How can you tell if there's a cycle in a linked list?

  3. Describe how you'd find the starting node of a cycle.

  4. Explain how to remove a Nth Node from the end of a linked list.

  5. How would you find the start of a loop?

  6. Describe the difference between an array data structure and a linked list.

  7. Explain the process of merging two sorted linked lists.

Programming questions about the binary tree

Here are 7 questions to do with the binary tree structure:

  1. When would you choose to use binary tree programming?

  2. Explain what leaf nodes are and why they are important.

  3. Define postorder traversal algorithm. How do you use it?

  4. Explain the difference: preorder, inorder and postorder traversals.

  5. Explain depth-first search algorithm as it applies to a binary tree.

  6. Can you traverse a binary tree in postorder traversal without recursion? Why, why not?

  7. Describe the process of leaf printing.

Programming questions about searching and sorting

Here are 7 searching and sorting questions for you to answer:

  1. You need to sort numbers. How do you write a program to do that?

  2. Describe the implementation differences for bubble sort and insertion sort in Java.

  3. Explain how you would implement a merge sort algorithm.

  4. Define a binary search algorithm. How would you use it in C++ vs. Java?

  5. Explain the difference between an unstable and a stable sorting algorithm.

  6. Can you explain what an Iterative Quick Sort algorithm is and how you would implement it?

  7. What is an insertion sort algorithm?

5 example programming interview questions with sample answers

Here are samples of programming interview questions and answers to help you prepare your own responses:

1. Explain the difference between a Java string and a string builder.

An interviewer asks this to check your understanding of string-based programming coding terms. Define the terms and mention their distinguishing features in your answer. Try to include technical, specific details to show your coding skills.

Example: 'A string is an unchangeable data type, also called finite. A string builder is a type of string that you can manipulate and change. Use string builders when you think you might want to update an array's character sequence.'

2. In an array of 1 to 100, how do you find a missing number?

An interviewer uses questions like this to assess the depth of your array programming knowledge and your grasp of its basic concepts. More complicated questions about duplicating arrays might follow this one. A good response to this question is to discuss the proper calculation of the number series.

Example: 'Find the missing number in an array of 1-100 by applying the formula n(n+1)/2 to the series and calculating the sum of the series.'

3. When is linked list programming most useful?

This is a simple question with the sole purpose of evaluating your understanding of linked list programming and how it relates to the larger context of computer programming. Use your answer to showcase your knowledge of this type of programming.

Example: 'If you have abstract types of data, linked list programming is the way to go. Linked lists make it simple to work with vectors, queues, stacks, trees or arrays. Links make it simpler to manipulate or delete them.'

4. How would you find the binary tree's depth?

This question is for the interviewer to gauge your understanding of coding practices and your ability to explain technical concepts simply.

Example: 'To find the depth of a binary tree, use the equation Dn=log 2 (n+1). First, find the maximum number of nodes existing in the binary tree and apply that number to the equation.'

5. Describe the key differences between the terms sorting and searching.

How you answer this question gives the interviewer insight into your understanding of industry terminology and if you can differentiate between the two concepts. Use your answer to define each concept individually and highlight what makes them different from one another.

Example: 'Searching is the process of looking for a particular element that matches certain criteria within an array. Sorting is a process that allows you to change the order of items in an array, to either ascending or descending. Searching identifies one element, whereas sorting creates order within a group of items.'

Practical coder interview tips

Here are some tips to help you succeed during your next coding interview:

  • Research the company you're applying for: Understanding the company's goals can help you customise your responses to fit the role. For example, you may highlight skills and experience you have that match the company's culture or mission.

  • Dress professionally: Try to find out the dress code from the company's social media or website if you aren't already familiar with it. If your interview is at a large company, you can show initiative by calling their HR department and asking about the dress code.

  • Plan your route to the interview: Make sure you know the interview location and exactly how long it takes to commute there. Give yourself extra time to allow for emergencies.

  • Practise body language and good manners: Move confidently, make eye contact and shake hands firmly to create a positive impression.

  • Be authentic and positive: Being yourself during an interview makes you more accessible to your interviewer. An optimistic outlook indicates you may be easy to work with.

  • Connect your answers back to your skills and experience: Use every question asked as an opportunity to tie in how your abilities fit to the job requirements.

  • Use the STAR method for answering practical questions: Using the STAR method (Situation, Task, Action and Result) frames your answers in a concise, practical way. This method works well when the interviewer asks for examples of how you used a particular skill.

  • Speak positively about your previous employer. Speaking constructively about your previous employer shows interviewers that you're professional.

  • End the interview effectively. You can ask about the next steps to happen in the interview process. Then end with a smile and a confident thank you .

Related: Improve Your Nonverbal Communication Skills

Jobs for coders, developers and programmers

If you have an aptitude for coding, programming and software development, there are many IT fields that you could go into. As you work in the industry, you may gain insight into the specific coder field best suited to your skill set. Here are some examples of jobs available for a coder:

  • analyst programmer

  • cloud engineer

  • game developer

  • software developer

  • medical coder

  • web developer

  • front end developer

  • full stack developer

  • systems administrator

  • mobile application developer

Please note that none of the companies mentioned in this article are affiliated with Indeed.

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