Medium data structure and algorithm practice puzzle.
Autotiling picks each wall's picture from its neighbors, so walls join up into smooth shapes on their own. Given a grid where 1 is a wall and 0 is empty, return a grid of tile numbers. An empty cell gets -1. A wall gets a 4-bit bitmask of which neighbors are also walls: add 1 for the one above, 2 for the right, 4 for below and 8 for the left. Those 16 numbers pick which of 16 tile pictures to draw. Cells off the edge of the grid count as empty.
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 Presence Filter, a pipeline you can run and download. See every Software Engineer project.
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