Easy data structure and algorithm practice puzzle.
Given a seed, return the next one: multiply by 1664525, add 1013904223, and keep the low 32 bits. That's a linear congruential generator, the oldest trick for repeatable random numbers. Same seed in, same seed out, on every machine. That's exactly what two players sharing one board need, because asking the machine for real randomness would give them different boards.
Solve it three ways: snap the jigsaw pieces together, fill in the blanks, or type it from scratch against the tests. This one is free.
Every line of the solution comes with a note explaining why it is there, and a step by step replay shows the code running. At level 3, where you type it yourself, you can ask for an AI mock interview on this problem that ends with a hiring manager's scorecard.
Then grow it into a real project with the Software Engineer button: this puzzle becomes the Reading Integrity Check, a pipeline you can run and download. See every Software Engineer project.
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