Shuffle an Array

class Solution {
private:
    vector<int> arr, idx;
public:

    Solution(vector<int> nums) {
        srand(time(NULL));
        idx.resize(nums.size());
        arr.resize(nums.size());
        for(int i = ; i < nums.size(); ++i)
        {
            arr[i] = nums[i];
            idx[i] = nums[i];
        }
    }

    /** Resets the array to its original configuration and return it. */
    vector<int> reset() {
        for(int i = ; i < arr.size(); ++i)
        {
            arr[i] = idx[i];
        }
        return arr;
    }

    /** Returns a random shuffling of the array. */
    vector<int> shuffle() {
        for(int i = arr.size() - ; i >= ; --i)
        {
            int j = rand() % (i + );
            swap(arr[i], arr[j]);
        }

        return arr;
    }
};

初始化种子一定要在类的构造函数里