Evaluating the technical skills of a candidate is not an easy task. For technical positions, especially where programming is involved, a code challenge is one of the ways to evaluate a candidate.
You will see many general code challenges involving arrays, LinkedList, sorting, and so on. While these coding challenges do evaluate candidates to some extent, real-world coding challenges are much better at evaluating candidates’ problem-solving skills.
Today we will share the top 5 coding challenges for interviews that can help hiring managers recruit the right candidate for the job. We will start with the process for creating a good coding challenge. Then we will suggest evaluation criteria for measuring candidates. In the end, we will share 5 coding challenges for online interviews to inspire your own hiring. We will also go through how you can evaluate the candidate for each of these coding challenges
Let’s dive in.
How to Design the Perfect Coding Challenge
Let’s look at a step-by-step process to design the perfect coding challenge for your needs.
1. Define the purpose
Before you start designing the challenge, it is essential to determine what you hope to achieve. Do you want to evaluate a candidate’s ability to write clean and efficient code? Do you want to test their analytical and problem-solving skills? Do you want to evaluate a candidate’s proficiency in a particular niche technology like Salesforce Apex? After you have identified the goals of the coding challenge, you will be in a better position to design it.
2. Keep it close to the real world
While it is okay to give general-purpose coding challenges like sorting an array or finding the missing number, if you give a real-world challenge that mimics the actual work they will be doing, that will generate more insights. It is perfectly possible that a candidate might not be able to solve a generic coding problem, but as soon as you give them a real-world problem, they can solve it successfully. So a combination of general-purpose quizzes and programming a real-world problem will be a good combination.
3. Choose the right problem
The coding challenge should be a problem that can be solved within an adequate amount of time. It should be neither very difficult nor easy but rather require a reasonable amount of effort and time to solve. Usually, a duration between 30 minutes to 90 minutes should be enough for most challenges.
Similarly, the problem should fall into the candidate’s area of expertise. There is no use in testing a candidate in an area they have not worked in. Asking a front-end developer to write a complex SQL query is such an example.
4. Specify any constraints
Provide clear guidelines for what the candidates should do. Specify the programming language, the time limit, the input and output format, any particular method to solve the problem, and so on.
5. Test the challenge
Before presenting the challenge to the candidate, test it yourself to make sure it is solvable and to verify that the constraints you have mentioned are appropriate. Note that there can be many solutions to solve a problem, and unless you have specified any particular solution, any solution presented by the candidate will be fine as long as it works under the constraints you specified.
6. Share your scoring criteria
It is also important to share your scoring criteria with the candidate beforehand. The scoring criteria will help the candidate focus on the essential areas of the solution. It is perfectly fine for scoring criteria to change depending on the coding problem to be solved. For example, code writing skills might be crucial for a developer position, but for a database administrator, you might be fine with a high-level algorithm instead of coding in a particular programming language.
7. Offer a helpful environment
Make sure that the environment in which the candidates are solving the challenge is as familiar as possible. Provide necessary tools, such as a relevant IDE, and ensure that they are stable and free from distractions.
Pro tip: The thought process is as important as the code
While writing clean and working code is essential for any coding challenge interview, the thought process behind the code is equally important. It is not necessary to write a 100% correct code for a candidate to be successful; if the candidate’s solution is correct, but the implementation of his solution is faulty, at least you will know that they have problem-solving skills. This is especially true for complex coding challenges.
By following these steps, you can design coding challenges for interviews that effectively evaluate a candidate’s technical skills and help you make informed hiring decisions.
How to Measure Candidate Skills
While designing a coding challenge for candidates needs a lot of thought and skills, correct evaluation is also important. Below are some of the points you should keep in mind when evaluating the candidates for a particular coding challenge:
- Code efficiency
How efficient is the candidate’s solution? Does it run in a reasonable amount of time and use a reasonable amount of resources (memory, CPU, storage, etc.)? Did the candidate write a lengthy solution that could have been implemented in fewer lines? - Code readability
Is the candidate’s code easy to understand and maintain? Is it well-documented and organized? Are methods and variables properly named? - Problem-solving approach
How did the candidate approach the problem? Did they break it down into smaller, manageable parts? Did they use appropriate algorithms and data structures? Did the candidate use the right approach to solve the problem? - Correctness
Does the candidate’s solution correctly solve the problem? Does it handle all cases and return the correct output for all inputs? Does the solution handle failure scenarios? - Thinking out of the box
Did the candidate come up with an innovative or unique solution to the problem? Did they demonstrate a deep understanding of the problem and the underlying algorithms and data structures?
Top 5 Coding Challenges to Recruit Developers
Find below some of the best live coding challenges to inspire your own.
Challenge #1
Eight teams participate in a football tournament. Each team plays against the other team exactly once. In each match, the winner gets 3 points and the loser does not get any points. If a match is a draw, each team gets 1 point. At the end of the tournament, the total number of points obtained by all the teams is X. What is the largest number of points that the winning team could obtain? Input will be the total points by all teams while output will be the largest number of points obtained by the winning team. Assume that no single team will win all the matches.
Evaluation guidelines
Check whether the candidate:
- Uses arithmetic calculations and variables correctly
Challenge #2
You have a table called “Developer_info” with the following attributes:
| Id | int |
| FirstName | object |
| LastName | object |
| Salary | Int64 |
| object | |
| Manager_Id | Int64 |
| Department | Object |
A similar table exists for Managers as well. You need to display the developer names who are earning more than their managers, along with corresponding salaries.
Evaluation guidelines
Check whether the candidate:
- Implements a JOIN clause of manager and developer tables
- Compares the salary of developers with managers
Challenge #3
David writes, in ascending order, all the numbers from X to 2022 which use only 0’s and 2’s. What is the number in the middle of the list? Input will be the number X while output will be the number in the middle of the list. Note that X will be always smaller than 2022.
Evaluation guidelines
Check whether the candidate:
- Uses different functions of the array correctly
Challenge #4
You have an unlimited number of packets having number stickers. Each packet has a total of 10 number stickers. These number stickers are 1,2,3,4,5,6,7,8,9,0. Each packet has the same 10 stickers with numbers from 0 to 9 without duplicates. If you have to display numbers from 1 to X affixing these stickers on a board, how many minimum packets would you need to open? Note that X will always be greater than 1. Input will be the number X and output will be the minimum number of packets to be opened.
Evaluation guidelines
Check whether the candidate:
- Takes into account the zeros and ones
Challenge #5
There is a room in which n lamps are placed in a row. At first, they are all off. In the first round, you turn on all the lamps. Then in the second round, you turn off every second lamp.
In the third round, you toggle every 3rd lamp (if it is off, you turn it on, or if it is on, you turn it off).
For the kth round, you toggle every kth lamp.
For the nth round, you toggle only the last lamp.
Return the number of lamps that are on after n rounds. Input will be the number of rounds and output will be the number of lamps that are ON.
Evaluation guidelines
Check whether the candidate:
- Uses a simple function of maths to solve the problem
Conclusion
Today we discussed how hiring managers can design a good code challenge. We also went through different evaluation parameters when assessing the candidates. In the end, we present some good interview code challenges which can help hiring managers shortlist the best candidates.
Further reading:
- Java Coding Interview Questions
- Python Coding Interview Questions
- ReactJS Coding Interview Questions
- JavaScript Coding Interview Questions
- C# Coding Interview Questions
- C++ Coding Interview Questions
- PHP Coding Interview Questions
- 73 Advanced Coding Interview Questions for Experienced Developers
