var arr = []
    // function random(s,e){
    //     return Math.floor(Math.random()*(e-s) + s)
    // }
    for(var i = 0;i<10000;i++){
        arr.push(++i)
    }
    function a(arr,num){
        if(arr.length === 0)return ;
        var low = 0;
        var high = arr.length - 1;
        while(low <= high){
            var mid = Math.floor((low+high)/2);
            if(arr[mid] === num){
                return mid;
            }else if(arr[mid] < num){
                high = mid -1;
            }else{
                low = mid +1;
            }
            return mid;
        }
        return -1
    }