二分查找

function search( nums ,  target ) {
    let start=0;
    let end=nums.length-1;
    let index=-1;
    while(start<=end){
        let middle=Math.floor((start+end)/2);

        if(nums[middle]==target){
            index=middle;
            end=middle-1;
        }

        if(nums[middle]<target){

            start=middle+1;

        }else{
            end=middle-1;
        }



    }

    return index
}