Easy data structure and algorithm practice puzzle.
Given a binary tree, return every value level by level, top to bottom and left to right. Use a queue. Start with the root. Each time, take a node off the front, record its value, and add its left and right children to the back. This is breadth-first search, and it needs a queue, not recursion.
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 Order Typeahead, a pipeline you can run and download. See every Software Engineer project.
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