Recursion

A recursive function calls itself on a smaller piece of the problem. It needs a base case that stops the calls and a recursive case that moves toward it. Recursion fits problems that are nested by nature, such as arrays inside arrays or folders inside folders.

How it reads

• Base case: n <= 1 answers without another call
• flatten recurses only into items that are arrays
• Each call waits for the smaller call, then builds its own answer

Cloud tip: Assume the smaller call already works, and only decide how to use its answer.