Easy data structure and algorithm practice puzzle.
Given a stream of keys and a max length, return what's left in the cache, oldest first. Add each key to the end. If the cache is now longer than the max, drop the oldest one from the front. This sliding window keeps a transformer's key-value cache from growing forever.
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 Request Smoothing Rig, a pipeline you can run and download. See every Software Engineer project.
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