Easy data structure and algorithm practice puzzle.
Given an index i in a heap stored as an array, and the heap's size, return [left child, right child]. The children are at 2i + 1 and 2i + 2. If a child's index is past the end of the heap, use -1 for 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 Track Streak Finder, a pipeline you can run and download. See every Software Engineer project.
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