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();

public class L384ShuffleanArray {



 private int[] nums;
 private Random random;

 public L384ShuffleanArray(int[] nums) {
  this.nums = nums;
  random = new Random();
 }

 /** Resets the array to its original configuration and return it. */
 public int[] reset() {
  return nums;
 }

 /** Returns a random shuffling of the array. */
 public int[] shuffle() {
  if (nums == null)
   return null;
  int[] a = nums.clone();
  for (int i = a.length; i >1; i--) {
   swap(a, i-1, random.nextInt(i));
  }
  return a;
 }

 private void swap(int[] a, int i, int j) {
  int t = a[i];
  a[i] = a[j];
  a[j] = t;
 }

 public static void main(String[] args) {
  L384ShuffleanArray test = new L384ShuffleanArray(new int[] {1,2,3,4,5,6});
  System.out.println(Arrays.toString(test.shuffle()));
  System.out.println(Arrays.toString(test.reset()));

 }