Medium data structure and algorithm practice puzzle.
Given packet numbers in the order they arrive, and the number you expect first, return how many packets you can deliver in order by the end. A packet that arrives early waits in a buffer until the gap in front of it fills, then a whole run may go out at once. Duplicates don't count twice.
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.
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