Hard data structure and algorithm practice puzzle.
Given a routing tree and an address as a list of bits, return the next hop of the most specific route that matches, or 0 if none does. A node holds a next-hop ID where a route ends, and 0 where it's just a branch. Walk down, going left on a 0 bit and right on a 1, and remember the last real route you passed. That's the longest prefix match, and every packet on the internet goes through it.
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 Taxonomy Builder, a pipeline you can run and download. See every Software Engineer project.
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