二分查找

let arr = [1,2,4,5,6,10,23,45,67];
function binarySearch(arr, value) {
    if(!(arr instanceof Array)) {
        return;
    }
    let left = 0, right = arr.length - 1;
    let index = Math.floor((left+right) / 2);
    let medium = arr[index];
    while(medium != value) {
        if(medium > value) {
            right = index - 1;
        }
        if(medium < value) {
            left = index + 1;
        }
        index = Math.floor((left+right)/2);
        if(index < left || index > right) {
            return -1;
        }
        medium = arr[index];
    }
    return index;
}