Typical Coding Interview Questions

We have interviewed tens of recruiters and hiring managers, and asked them what are the most common questions that candidates struggle with. We also did extensive research online to find out the most common questions. In this article we go through our findings, so you don't have to worry about what to expect. We also give you some tips on how to answer these questions, so you can walk into your interview with confidence.

The most common questions

Traditional coding interviews usually have the same type of questions. These questions are not random: they are designed to test how you think and how you approach problem solving.

Here are the most common categories that these questions fall into:

1. Data Structures and Algorithms

Data Structures and Algorithms are the basic building blocks of coding. This is why it is very likely that you will be asked about them. Most often the interviewers want to see if you can use the basic coding tools, like arrays, linked lists and trees.

Here are some of the questions that you should prepare for:

"Reverse a linked list."
"Find the maximum depth of a binary tree."
"Shift all elements of a circular array by k bytes, using no extra memory."

These questions are asked because t hey show if you really understand how to organise and manipulate date efficiently. They basically want to see if you can write smart code.

2. Dynamic Programming

Dynamic programming sounds fancy, or even scary, but it's really just one way to solve problems. Dynamic programming involves breaking the problems down into smaller pieces, and solving them one-by-one. These questions are common in interviews because they test how your ability to split problem into smaller parts.

"Find the longest increasing subsequence in an array."
"Calculate the minimum cost to climb stairs."

These questions are a bit of a brain workout. But when you nail them, you really show that you can handle complex problems by simplifying them.

3. System Design

System Design questions are usually asked for more senior programmer roles. These questions are not about small coding tasks, but about designing big systems or applications that deal with a lot of data.

"Design a GPS navigation unit for a hiker": This question tests how you would build a device that works well in the wild, possibly with limited access to GPS satellites and without a constant power source.
"Design a communication device for Canadian park rangers": This one is about creating a reliable way for park rangers to communicate in remote areas, which means thinking about range, battery life, and durability.
"Design a URL shortening service like bit.ly": This asks how you would build a service that turns long URLs into short ones while handling millions of users.

These questions help interviewers see if you can think big and create systems that are efficient, reliable, and scalable.

Why companies ask these same questions?

The goal of these questions isn't just to be annoying to the candidate. They are used to see how you approach problem solving, how you structure your thoughts, and what kind of solutions you come up with. On the job, you will often face challenges that you didn't expect. These questions are a way to simulate that experience.

General Tips

Here is our list of top tips to help you prepare for your coding interview:

Practice Regularly: Use sites like LeetCode, HackerRank, and others to practice problem solving. The more you solve problems, the better you'll get at spotting patterns and coming up with solutions quickly.
Explain Your Thinking: During the interview, talk about your thought process. This shows the interviewer how you are approaching the problem, and help them see your logic.
Stay Calm: If you get stuck, don't worry. Take a deep breath, and break the problem into smaller parts. Even if you don't get to the final solution, showing progress is important.
Ask Questions: If something isn't clear about the problem, ask for clarification. In the real job you don't have all the answers either, so it is important that you reach out for help when facing a blocker.

References

LeetCode: "Top Interview Questions"
Glassdoor: "15 Must-Know Java Interview Questions & Answers"
HackerRank: "Interview Preparation Kit"