Hard data structure and algorithm practice puzzle.
Given a song's lines, return the line that shows up most often. Count each line in a hash map as you go, and update your best line whenever one passes the current top count. If two lines tie, the one that hit that count first wins. A song with one line returns that line.
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 Track LRU Service, a pipeline you can run and download. See every Software Engineer project.
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