8ee50178f3
Correct: `Array.from()` (it’s a static method) Incorrect: `Array.join()` (doesn’t exist; it’s a prototype method) This patch uses the common `#` syntax to denote `.prototype.`.
25 lines
1.2 KiB
Markdown
25 lines
1.2 KiB
Markdown
### binarySearch
|
|
|
|
Use recursion. Similar to `Array.prototype.indexOf()` that finds the index of a value within an array.
|
|
The difference being this operation only works with sorted arrays which offers a major performance boost due to it's logarithmic nature when compared to a linear search or `Array.prototype.indexOf()`.
|
|
|
|
Search a sorted array by repeatedly dividing the search interval in half.
|
|
Begin with an interval covering the whole array.
|
|
If the value of the search is less than the item in the middle of the interval, recurse into the lower half. Otherwise recurse into the upper half.
|
|
Repeatedly recurse until the value is found which is the mid or you've recursed to a point that is greater than the length which means the value doesn't exist and return `-1`.
|
|
|
|
```js
|
|
const binarySearch = (arr, val, start = 0, end = arr.length - 1) => {
|
|
if (start > end) return -1;
|
|
const mid = Math.floor((start + end) / 2);
|
|
if (arr[mid] > val) return binarySearch(arr, val, start, mid - 1);
|
|
if (arr[mid] < val) return binarySearch(arr, val, mid + 1, end);
|
|
return mid;
|
|
};
|
|
```
|
|
|
|
```js
|
|
binarySearch([1, 4, 6, 7, 12, 13, 15, 18, 19, 20, 22, 24], 6); // 2
|
|
binarySearch([1, 4, 6, 7, 12, 13, 15, 18, 19, 20, 22, 24], 21); // -1
|
|
```
|