Hard data structure and algorithm practice puzzle.
Given a ray's origin o and unit direction d, and a sphere's center c and radius r, return the distance t to the nearest hit in front of the ray, rounded to 4 decimals, or -1 for a miss. Plugging the ray into the sphere's equation gives a quadratic in t. If the discriminant is negative, it misses. Otherwise, take the smaller root. If that's behind the ray, return -1.
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 Sampler, a pipeline you can run and download. See every Software Engineer project.
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