Medium data structure and algorithm practice puzzle.
Physical memory is tracked as a bitmap, one entry per page: 0 is free and 1 is in use. Given the bitmap and a number of pages k, return the index of the first run of k free pages in a row, or -1 if there is none. Some allocations have to be physically contiguous, such as a buffer a device writes into directly, and plenty of free memory is no help if it is scattered in pieces smaller than k. That is external fragmentation.
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.
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