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###### Seokhyun Wie

**Full Stack JavaScript**Techdegree Graduate 21,594 Points

# JavaScript Recursive Binary Search

```
const recursive_binary_search = (array, target) => {
if (array.length == 0) {
return false;
} else {
const midpoint = Math.floor(array.length / 2);
if (array[midpoint] == target) {
return true;
} else {
if (array[midpoint] < target) {
const newArray = array.filter((num) => num > array[midpoint]);
console.log(newArray);
return recursive_binary_search(newArray, target);
} else {
const newArray = array.filter((num) => num < array[midpoint]);
console.log(newArray);
return recursive_binary_search(newArray, target);
}
}
}
};
const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
const result = recursive_binary_search(numbers, 10);
console.log(result);
```

I don't see Recursive Binary Search JavaScript version here, but only has plain Binary Search one.
For some of you who learned only JS at this point and want to know how it works, you can copy and paste this code and run it.
I added a couple of `console.log`

s so that you can visualize how arrays are forming step by step. You can play with changing target numbers at the bottom. Happy Coding!

## 2 Answers

###### Mike Straw

7,064 PointsSince the main Python code was rewritten to account for the cost of `array.slice()`

, I built my `recursive_binary_search.js`

like this:

```
function recursive_binary_search( list, target, start = 0, end = false ) {
if ( ! end ) {
end = list.length - 1;
}
if ( start > end ) {
return false;
} else {
mid = Math.floor( ( ( start + end ) / 2 ) );
if ( target === list[mid] ) {
return mid;
} else if ( target < list[mid] ) {
return recursive_binary_search( list, target, start, mid - 1 );
} else {
return recursive_binary_search( list, target, mid + 1, end );
}
}
}
```

###### Seokhyun Wie

**Full Stack JavaScript**Techdegree Graduate 21,594 Points

Gia Chan Yeah, I just wanted to code to look similar, but I never thought about that. Here: Medium, I could find some comparisons; however, nothing was mentioned regarding the time-complexity, but also Here: StackOverflow, someone claims that the `array.slice()`

has linear runtime complexity, O(n). I just got into this algorithm course two days ago, so I need some more research on this . Thanks for your insight.

###### Gia Chan

**Full Stack JavaScript**Techdegree Student 2,762 Points

Thanks for your sharing. I just got into this two days ago too, keep going and enjoy!

## Gia Chan

Full Stack JavaScriptTechdegree Student 2,762 Points## Gia Chan

Full Stack JavaScriptTechdegree Student 2,762 Pointsbut .filter is linear runtime? i think the correct answer is below. function recursive_binary_search(list, target) { if (list.length === 0) { return false; } else { let midpoint = Math.floor(list.length / 2);

} }