1. void randomCards(vector<int> &arr){
    2.     int index = 0, len = arr.size();
    3.     srand((unsigned)time(NULL));
    4.     for(int i = len - 1;i > 0;--i){
    5.         index = rand() % (i + 1);
    6.         swap(arr[index], arr[i]);
    7.     } 
    8. }