Easy data structure and algorithm practice puzzle.
Given n stairs, return how many different ways you can climb to the top taking 1 or 2 steps at a time. Your last move was either 1 step or 2, so the ways to reach step n are the ways to reach n - 1 plus the ways to reach n - 2. That's the Fibonacci sequence. Build it up from the bottom with two variables.
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 Sample Capacity Planner, a pipeline you can run and download. See every Software Engineer project.
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