Hard data structure and algorithm practice puzzle.
Given a routing tree where each node holds a next-hop ID, or 0 for no route, return how many nodes have two children that could be merged into it. Two children can be merged when both exist and point to the same next hop. Two zeros don't count, since that's two nodes with no route at all. Count every merge spot in the tree.
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.
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