Easy data structure and algorithm practice puzzle.
Given a list of daily prices, return the most money you can make by buying on one day and selling on a later day. If prices only fall, return 0. Walk the list once and keep track of the lowest price so far. On each day, check what you'd make selling today, and keep the best. You never need to look back further than that one number.
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 Trade Budget Allocator, a pipeline you can run and download. See every Software Engineer project.
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