Easy data structure and algorithm practice puzzle.
Given an array of bits, return the number it represents. Start at 0. For each bit, double what you have and add the bit. Every step to the left is one more power of two, so [1, 0, 1] is 4 + 0 + 1 = 5. The same loop reads numbers in any base.
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 Shot Flag Store, a pipeline you can run and download. See every Software Engineer project.
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