384. Shuffle an Array

Shuffle a set of numbers without duplicates.

Example:

// Init an array with set 1, 2, and 3.
int[] nums = {1,2,3};
Solution solution = new Solution(nums);

// Shuffle the array [1,2,3] and return its result. Any permutation of [1,2,3] must equally likely to be returned.
solution.shuffle();

// Resets the array back to its original configuration [1,2,3].
solution.reset();

// Returns the random shuffling of array [1,2,3].
solution.shuffle();

class Solution {
public:
    Solution(vector<int>& nums) : arr(nums) {
        srand(time(NULL));
    }
    
    /** Resets the array to its original configuration and return it. */
    vector<int> reset() {
        return arr;
    }
    
    /** Returns a random shuffling of the array. */
    vector<int> shuffle() {
        vector<int> res = arr;
        for (int i = 0; i < res.size(); ++i) {
            // int j = i + rand() % (res.size() - i);
            int j = rand() % (i + 1);
            swap(res[i], res[j]);
        }
        return res;
    }
private:
    vector<int> arr;
};