Medium data structure and algorithm practice puzzle.
Given balloons as [start, end] spans on a line, return the fewest arrows to pop them all. An arrow at x pops every balloon whose span includes x. Sort by end. Shoot at the first balloon's end, and that arrow pops every balloon that starts at or before that spot. When you reach one that starts after it, shoot again at its end.
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 Ticket Calendar Merger, a pipeline you can run and download. See every Software Engineer project.
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