Medium data structure and algorithm practice puzzle.
Given two bit arrays of the same length, return how many positions differ. Walk them side by side and count the mismatches. Error-correcting codes are built around this number: if every pair of valid codes is at least 3 apart, any single flipped bit can be fixed.
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 Streak Finder, a pipeline you can run and download. See every Software Engineer project.
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