Hard data structure and algorithm practice puzzle.
Given a list of [start, end] bookings, return true if any two overlap. Ending at 3 and starting at 3 is fine. Sort the bookings by start time. Then each one only needs to be checked against the one right before it. If it starts before that one ends, they overlap. That's a sort plus one pass instead of checking every pair.
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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