How to Ace McKinsey HackerRank Test in 2025 With Easy Tricks

Mckinsey HackerRank Test Questions

I just finished McKinsey's 2025 HackerRank test. Below are the actual questions I encountered and how I solved them.

SQL Query Question

The task was to query the names of plants that only thrive in one type of weather and their corresponding weather types, using data from two tables: plant and weather.

My first instinct was to rely on table joins and grouping. I started by doing an inner join between the plant table’s SPECIES field and the weather table’s PLANT_SPECIES field to link the two datasets. After grouping the results by plant name, I filtered for groups where COUNT(DISTINCT weather.TYPE) was 1, this gave me exactly the plants tied to a single weather type.

Graph Theory Algorithm Question

The problem involved multiple computers, some already connected by cables into groups. We could perform one operation: remove a cable between two computers and connect another pair. We needed to find the minimum number of operations to connect all computers, or return -1 if it was impossible.

I knew right away the Union-Find algorithm was the solution here. Using it, I counted the initial number of connected components. If there was only 1 component, all computers were already connected, so I returned 0. If cables were fewer than (number of computers - 1), connection was impossible, so -1 went into the answer. For other cases, the minimum operations were the component count minus 1—each operation cuts the component number by one indirectly.

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Frontend Development Question

The task was to use vanilla JavaScript to add 20 horizontally arranged buttons to a div with the id "button-container". Each button needed an id from 1 to 20, and clicking a button should alert its index.

I first grabbed the target container with getElementById, then set up a for loop from 1 to 20. Inside the loop, I created a button, set its id to the loop variable i, and labeled it "Button #i" with innerText. I also bound a click event to make it alert the index. Nerves got to me a little, though, so I had to debug the code a few times before it worked.

REST API Call Question

We needed to call a paginated API for university data to retrieve and process information about universities worldwide. The API URL was https://jsonmock.hackerrank.com/api/universities, and we had to handle pagination logic.

This felt familiar, similar to a HubSpot OA question I’d done before, but easier. I sent a GET request for the first page first, pulling out total_pages from the response. Then I looped through all page numbers, fetching each one, extracting university info from the data array, and focusing on organizing key fields like country. The whole data aggregation part went pretty quickly for me.

Mckinsey HackerRank Test Format

My personal interview format was as follows. It had 4 questions total, with a 100-minute time limit, covering data processing, algorithms, frontend development, and API calls. It was really comprehensive for assessing the skills needed for a data engineer role.

However, you might encounter other formats depending on the role you're applying for. Below is a more general McKinsey HackerRank test format.

Question Types

The test usually gives you two Python coding questions and two SQL coding questions. You get 120 minutes to finish everything. The questions come in two main types: multiple choice and coding tasks.

Below are the difficulty levels of different types of interview questions:

Most questions focus on arrays and strings. They don’t go too deep into advanced algorithms, so I focus my practice on these areas. The SQL questions often ask me to write queries using SQL Studio, while the Python questions use a built-in IDE.

Practice Methods

I always start my prep by finding shared resources and previous questions. Practicing with old questions helps me get familiar with the test format. It also calms my nerves because I know what to expect. Here’s what I get out of practicing previous test questions:

• I become familiar with the test format, which helps me feel less anxious.

• I learn about different question types and develop strategies for each.

• I spot my strengths and weaknesses, so I know where to focus.

• Regular practice improves my time management skills.

• My skills improve, and my performance gets better.

• I feel more prepared and in control, which reduces test anxiety.

• I can customize my study plan to fit my needs.

I also try to simulate the test environment by using the same IDEs and time limits.

Another highly recommended tool is Linkjob.ai. If you haven't practiced sufficiently, or if you're unable to solve problems due to various unexpected situations, you can directly take a screenshot and let the AI generate answers for you. Moreover, it will present the answer framework to you in the form of bullet points. If you still feel very uncertain, you can even directly copy the AI-generated code. And the best part is that interviewers won't find out.

Time Tips

Time management makes a huge difference in the mckinsey hackerrank test. I always set a timer when I practice. I give myself 30 minutes for each question. This helps me stay on track and avoid spending too long on one problem.

I read every question carefully before I start coding. If I get stuck, I move on and come back later. I keep my code simple and avoid overthinking. I also use the built-in IDE features, like syntax highlighting and auto-complete, to save time. When I finish a question, I quickly check my code for errors before moving on.

Coding Approach

Language Choice

I always start by picking the right language for the job. I stick with Python for coding questions because it is simple and powerful. Python lets me write less code to do more.

Here’s how I decide which language to use:

• I choose Python for logic, arrays, and string problems.

• I use SQL for anything that involves tables or data queries.

• I avoid switching languages during the test.

Tip: Practice both Python and SQL before test day. Get comfortable with their syntax and quirks.

Clean Code

Writing clean code saves me time and helps me avoid mistakes. I always keep my code readable. I use clear variable names and add comments when something is tricky. I break big problems into smaller steps.

Here’s my checklist for clean code:

1. Use simple, short variable names that make sense.

2. Write one function for each task.

3. Add comments for any tricky logic.

4. Keep my code organized with spaces and indentation.

For example, when I solve a Python problem, I write code like this:

def count_even_numbers(arr):
    count = 0
    for num in arr:
        if num % 2 == 0:
            count += 1
    return count

This code is easy to read and debug. I avoid clever tricks that make code hard to follow.

Debug Fast

Debugging quickly is a must for the mckinsey hackerrank test. I use a step-by-step approach to find and fix bugs.

Here’s what I do:

• I read the error message carefully. It usually tells me where the problem is.

• I add print statements to check my variables and logic.

• I test my code with simple inputs first. If it works, I try edge cases.

I always keep my code simple. The fewer lines I write, the fewer places bugs can hide. I practice debugging before the test so I can fix problems fast under pressure.

Prep Tools

Online Resources

I always start my prep with the right online resources. I look for coding platforms that offer Python and SQL practice problems. Sites like LeetCode and HackerRank help me sharpen my skills. I also check out YouTube tutorials when I get stuck on a topic. These videos break down tough concepts into simple steps. I bookmark helpful blog posts and guides so I can review them before the test.

Mock Tests

Taking mock tests gives me a real sense of what to expect. I set up a quiet space, use a timer, and try to finish four questions in 100 minutes. Mock tests show me where I need to improve. I review my mistakes and try again until I get it right. This routine builds my confidence and speed.

My personal recommended mock interview platform is Linkjob. Its mock interview question bank is compiled based on a wealth of real interview experiences, making it extremely comprehensive. Additionally, it can provide personalized mock interviews tailored to your resume and the position you're applying for.

Peer Support

Studying alone can feel tough. I reach out to friends who are also preparing for the mckinsey hackerrank test. We share resources, swap practice questions, and talk through tricky problems. Sometimes, I join online forums or Discord groups. These communities offer support and fresh ideas.

When I explain my solutions to others, I understand the material better. I also learn new approaches from my peers. Working together keeps me motivated and makes studying more fun.

FAQ

How hard is the McKinsey HackerRank test?

I found the test challenging but fair. Most questions focus on arrays, strings, and SQL basics. If you practice these topics, you’ll feel more confident. Don’t worry about advanced algorithms.

Can I retake the test if I don’t pass?

Usually, McKinsey allows only one attempt per application cycle. I always double-check the rules before applying. If I don’t pass, I use the experience to prepare better for next time.