Hard data structure and algorithm practice puzzle.
Given daily revenue, return the most days in a row that revenue went up from the day before. So [1, 2, 3, 2, 4] is 2, and a list that only falls is 0. Walk through once and compare each day with the one before. If it went up, add one to your streak. If not, reset the streak to 0. Keep the best streak you see.
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 Order Integrity Check, a pipeline you can run and download. See every Software Engineer project.
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