[TOC]
# Binary Search Algorithm
```
// 來自 https://www.cnblogs.com/Answer1215/category/534566.html
// 使用 TypeScript
function binarySearch (
array: number[],
element: number,
start: number = 0,
end: number = array.length - 1
):number {
if(end < start) return -1;
const middle = Math.floor((start + end) /2);
return element === array[middle] ?
middle :
element < array[middle] ? binarySearch(array, element, start, middle -1) : binarySearch(array, element, middle + 1, end);
}
const unsortedArray = [6, 7, 8, 9, 10, 1, 2, 3, 4, 5]
console.log("12312312: ", unsortedArray.sort()) // 注意這里的 sort 的結果：[1, 10, 2, 3, 4, 5, 6, 7, 8, 9]
console.log("index of 4: ", binarySearch(unsortedArray.sort(), 4))
console.log("22 not found: ", binarySearch(unsortedArray.sort(), 22))
```
