Easy data structure and algorithm practice puzzle.
Given a binary tree, return its biggest value, or null if it's empty. It's not a search tree, so there's no shortcut. Every node has to be checked. Take the biggest of the node's own value and what each subtree reports. Start with the node's value, not 0, or a tree of negatives gives the wrong answer.
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 Login Typeahead, a pipeline you can run and download. See every Software Engineer project.
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