RACKlette Recruiting Task

Welcome to Team RACKlette's recruiting challenge!

At the end of this challenge, you can retrieve the link for signing up an interview with us from the puzzle. Have fun :)

We are a student HPC team at ETH Zurich working on high-performance computing, parallel programming, and system optimization. This small task gives you a first taste of the concepts we work with -- and helps us see that you are curious and motivated enough to follow through.

It should take 10-20 minutes. No prior HPC knowledge needed.

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Prerequisites

You need Git, a C compiler, and make. Check if they are already installed by opening a terminal and running:

git --version
gcc --version
make --version

How to open a terminal:

• macOS: press Cmd + Space, type Terminal, hit Enter
• Linux: press Ctrl + Alt + T, or search for Terminal in your apps
• Windows: install WSL (Windows Subsystem for Linux), then open the Ubuntu app it provides. All commands below are then run inside that Ubuntu terminal.

If any of the version commands fail, install the missing tools:

OS	Command
Ubuntu / Debian (incl. WSL)	sudo apt install git build-essential
macOS	xcode-select --install (installs git, gcc, and make in one go)
Fedora / RHEL	sudo dnf install git gcc make

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Step-by-step instructions

Step 1 — Clone the repository

In your terminal, navigate to a folder where you want to keep the task (e.g. your home directory or Desktop), then clone the repo:

cd ~
git clone https://github.com/Team-RACKlette/recruiting-task.git
cd recruiting-task

You are now inside the project folder. All subsequent commands should be run from this same folder.

Tip: you can confirm you are in the right place by running ls. You should see task.c and Makefile listed.

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Step 2 — Read task.c

Open task.c in any text editor — for example:

# macOS / Linux
open task.c          # opens in your default editor on macOS
nano task.c          # simple terminal editor on Linux/macOS/WSL

Or just open it with VS Code, Notepad++, or whatever editor you prefer.

Read the comment block at the top of the file. It explains what the program does and gives you a direct hint for solving it.

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Step 3 — Edit task.c

Find the line that says:

#define TILE_SIZE 1    /* <-- change this */

Replace 1 with the value you think is correct (the hint in the file tells you how to figure it out). Save the file.

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Step 4 — Compile

Back in your terminal (make sure you are still in the project folder), run:

make

This compiles task.c into an executable called task. If you see Build successful! you are ready for the next step. If you see an error, double-check that you saved the file and that gcc is installed.

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Step 5 — Run the program

./task

The ./ tells your terminal to run the task file that is in the current folder (as opposed to searching for a system command called task).

The program will print your checksum and compare it to the magic value.

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Step 6 — Iterate until it matches

If the checksums do not match, go back to Step 3, try a different value for TILE_SIZE, save, and repeat from Step 4. There are only a handful of valid options — you will get there quickly.

When the checksum matches, the program prints the interview sign-up link. Follow it to book your interview slot. Good luck!

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Troubleshooting

make: command not found — install the prerequisites listed above.

./task: Permission denied — run chmod +x ./task and try again.

make succeeds but the program crashes — make sure TILE_SIZE evenly divides 64 (the matrix size). Valid values: 1, 2, 4, 8, 16, 32, 64.

Nothing changes after editing — make sure you saved the file before running make. make will only recompile if the file has changed.

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-- Team RACKlette