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Let’s say you work at NASA and need to program a countdown function for launching spacecraft. The particular function that you’re asked to write should accept a number—such as 10—and display the numbers from 10 down to 0. Take a moment and implement this function in the language of your choice. When you’re done, read on.

Odds are that you wrote a simple loop, along the lines of this JavaScript implementation:

 ​ ​function​ countdown(number) { ​ ​for​(​var​ i = number; i >= 0; i--) { ​ console.log(i); ​ } ​ } ​ countdown(10);

There’s nothing wrong with this implementation, but it may have never occurred to you that you don’t have to use a loop.

How?

Let’s try recursion instead. Here’s a first attempt at using recursion to ...

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