Hard data structure and algorithm practice puzzle.
Given a grid where 0 is open and 1 is a wall, a start, and an end, return the fewest steps from start to end, moving up, down, left, or right. If you can't get there, return -1. Use breadth-first search with a queue, tracking the steps taken to reach each cell. Every step costs the same, so the first time you reach the end is the shortest way.
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 Blast Radius, a pipeline you can run and download. See every Software Engineer project.
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