Medium data structure and algorithm practice puzzle.
Given base, exp, and mod, return base to the power exp, mod m, without the number blowing up. Use exponentiation by squaring. While exp is above 0: if exp is odd, multiply the result by base. Then square base and halve exp. Take mod after every multiply to keep things small. This is the exact operation RSA encryption runs.
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 Reading Permission Mask, a pipeline you can run and download. See every Software Engineer project.
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