class Solution {
public:
    vector<int> res;
    Solution(vector<int>& nums) {
        res = nums;
    }
    
    int pick(int target) {
        int c = 0;
        int index = 0;
        for (int i = 0; i < res.size(); ++i){
            if (res[i] == target){
                c++;
                if (rand() % c == 0) index = i;
            }
        }
        return index;
    }
};