Hard data structure and algorithm practice puzzle.
Given gas stations as [position, fuel], your starting fuel, and a target distance, return the fewest stops to reach the target, or -1 if you can't. One unit of fuel goes one unit of distance. Drive as far as you can. When you'd run out, go back and pretend you stopped at the biggest station you passed. Choosing late is what makes this greedy approach work.
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 Packet Capacity Planner, a pipeline you can run and download. See every Software Engineer project.
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