Leetcode: 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();

Random random = new Random();

random.nextInt(int i);

 public class Solution {
     int[] arr;
     Random random;

     public Solution(int[] nums) {
         arr = nums;
         random = new Random();
     }

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

     /** Returns a random shuffling of the array. */
     public int[] shuffle() {
         int[] copy = arr.clone();

         for (int i=arr.length-1; i>=0; i--) {
             int index = random.nextInt(i+1);
             int temp = copy[index];
             copy[index] = copy[i];
             copy[i] = temp;
         }
         return copy;
     }
 }

 /**
  * Your Solution object will be instantiated and called as such:
  * Solution obj = new Solution(nums);
  * int[] param_1 = obj.reset();
  * int[] param_2 = obj.shuffle();
  */