384. Shuffle an Array

class Solution {
    vector<int> arr, idx;
public:
    Solution(vector<int> nums) {
        srand(time(NULL));
        arr = nums;
        idx.assign(nums.begin(), nums.end());
    }

    /** Resets the array to its original configuration and return it. */
    vector<int> reset() {
        arr.assign(idx.begin(), idx.end());
        return arr;
    }

    /** Returns a random shuffling of the array. */
    vector<int> shuffle() {
        for (int i = arr.size() - 1; i > 0; i--)
            swap(arr[i], arr[rand() % (i + 1)]);
        return arr;
    }
};

/**
 * 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();
 */

おまけ

random numbers

srand(time(NULL));
num = rand()%i;//get random numbers in [0, i)

for (int i = arr.size() - 1; i > 0; i--)
    swap(arr[i], arr[rand() % (i + 1)]);

get random k-permutation of the n elements in nums[n] into an new array pmt[k]

vector<int> getRandomKPermutation(){
    int n = 10, k = 8, randkey;
    int nums[10] = {1, 4, 45, 5, 6, 5, 9, 11, 1, 40};
    int len = n;
    vector<int> pmt;
    srand(time(NULL));
    for(int i = 0; i < k; i++){
    randkey = rand()%len;
    swap(nums[--len], nums[randkey]);
    pmt.push_back(nums[len]);
    }
    return pmt;

}