# Recursion: A Programming Concept

If you studied computer science or you're into programming, you most likely have come across the term *Recursion*. Quite a number of developer don't really use recursion, or perhaps it's the ones I know that don't use it. ๐ค๐ค

So, what is recursion?

Recursion is an iteration technique where a function calls itself. It's applicable when you need to call the same function repeatedly with different parameters from within a loop.

Search for *Recursion* on google and you get this.
Now, click against the suggested *recursion*.

What happens? You're redirected to the same page. That's recursion with a sense of humour.

## Recursion vs Loop

Let's take a look at 2 scenarios

Scenario A- Loop

```
const pow = (x,n)=>{
let result = 1;
for (let i = 0; i < n; i++) {
result *= x;
}
return result;
}
console.log( pow(2, 3) ); // 8
```

Scenario B- Recursion

```
const pow = (x,n)=>{
if (n == 1) {
return x;
} else {
return x * pow(x, n - 1);
}
}
console.log( pow(2, 3) ); // 8
```

What do you note between these 2 scenarios?
In scenario A, we *loop* over the variables i.e instructions are repeatedly executed while in scenario B, the function calls itself.

To calculate pow(2, 3) the recursive steps are as below:

pow(2, 3) = 2 * pow(2, 2) => 2 * 4 = 8

pow(2, 2) = 2 * pow(2, 1) => 2 * 2 = 4

pow(2, 1) = 2

Recursion reduces a function call to a simpler one until the result is gotten.

It's essential to define a breakpoint (`n==1`

as in the example above) else your function will run indefinitely.

## Differences between Recursion and Loops

**Time:**Recursion is more time consuming than loops.**Usage:**Recursion is used when code size needs to be small, and time complexity is not an issue. A loop is used when time complexity needs to be measured against the code size.**Termination:**Recursive function is terminated when there is no function call. A loop is terminated when the condition for the iterator ceases to be satisfied.

## Application of Recursion

- Fractal maths
- Sorting
- Traversing the nodes of complex or non-linear data structure
- File trees

## Conclusion

Recursion is a powerful technique and is the most direct way to solve a complex problem. However, due to its shortcomings, we will need to be very careful about how and where we apply recursion.

## References

- Recursion in Functional JavaScript
- Understanding Recursion Using Real-World Examples
- Difference between Recursion and Iteration
- Recursion and stack

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Ciao๐๐ผ

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