要求:洗牌随机
思路:在[i,n-1]的随机选一个与i交换

class Solution {
public:
    vector<int> origin;
    vector<int> current;
    int n;

    Solution(vector<int>& nums) {
        origin = nums;
        current = nums;
        n = nums.size();
    }
    
    vector<int> reset() {
        current = origin;
        return current;
    }
    
    vector<int> shuffle() {
        for (int i = 0; i < n; i++) {
            int tmp;
            int target = i + rand() % (n - i);
            tmp = current[i];
            current[i] = current[target];
            current[target] = tmp;
        }
        return current;
    }
};

/**
 * Your Solution object will be instantiated and called as such:
 * Solution* obj = new Solution(nums);
 * vector<int> param_1 = obj->reset();
 * vector<int> param_2 = obj->shuffle();
 */