Medium data structure and algorithm practice puzzle.
Given a list of lookups and a cache size, count how many lookups were hits. On a hit, move that key to the newest end. On a miss, add it there, and if the cache is now over size, drop the oldest key. This tells you whether the cache is earning its memory. Watch the case where you cycle through one more key than the cache holds: it never hits at all.
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 Trip Fuzzy Matcher, a pipeline you can run and download. See every Software Engineer project.
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