Medium data structure and algorithm practice puzzle.
Enemies spawn at the given spots along a straight lane, in no particular order. A tower placed at x covers everything from x - r to x + r. Return the fewest towers that cover every spawn. Sort the spots, then make the greedy choice: the leftmost uncovered spot has to be covered by something, and the best tower for it sits r to its right, covering up to that spot plus 2r. Skip everything that covers, then repeat.
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 Slot Packer, a pipeline you can run and download. See every Software Engineer project.
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