二分法查找

//二分法查找的前提，数组需要是有序的

function getIndex(arr,num){
    var len = arr.length,
        st  = 0,
        end = len-1
        while(st<=end){
        var mid = Math.floor((st+end)/2)
        if(num==arr[mid]){
            return mid
        }else if(num>arr[mid]){
            st = mid+1
        }else{
            end = mid-1
        }
    }
    return arr;
}
var ary=[1,4,7,8,12,34,67,88,99,100]

    <script>
        var a = [1,3,5,7,9,11,13,15];
        var min = 0;
        var max = a.length - 1;
        var findNum = 11;
        while(min <= max){
            var middle = parseInt((min+max)/2);
            if(findNum > a[middle]){
                min = middle + 1;
                middle = parseInt((min+max)/2);
            }
            else if(findNum < a[middle]){
                max = middle - 1;
                middle = parseInt((min+max)/2);
            }
            else{
                console.log("找到了"+middle);
                break;
            }
        }
    </script>