Easy data structure and algorithm practice puzzle.
Each object has a layer, one bit saying what it is, and a mask, a bitmask of every layer it reacts to. Given the layer and mask of two objects, return true if they collide. Both have to agree: A's mask must include B's layer, and B's mask must include A's layer. Check each one with a bitwise AND. That's how a player's bullets pass through the player but still hit enemies.
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 Entity Permission Mask, a pipeline you can run and download. See every Software Engineer project.
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