Medium data structure and algorithm practice puzzle.
Given a list of values and a buffer size, return what's in the buffer at the end, oldest first. Add each value. If the buffer is over its size, drop the oldest. That's a ring buffer, a fixed-size buffer where new items push out the oldest.
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 Retention Curve, a pipeline you can run and download. See every Software Engineer project.
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