Medium data structure and algorithm practice puzzle.
Given an m by n grid, return how many routes a robot can take from the top-left corner to the bottom-right if it can only move right or down. Each cell can only be reached from above or from the left, so its count is the sum of those two. The top row and left column are all 1s. Build it one row at a time.
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 Frame Forecaster, a pipeline you can run and download. See every Software Engineer project.
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