# 384. Shuffle an Array

## 1. Question

Given an integer array nums, design an algorithm to randomly shuffle the array. All permutations of the array should be equally likely as a result of the shuffling.

Implement the Solution class:

• Solution(int[] nums) Initializes the object with the integer array nums.
• int[] reset() Resets the array to its original configuration and returns it.
• int[] shuffle() Returns a random shuffling of the array.

## 2. Examples

Example 1:

Input
["Solution", "shuffle", "reset", "shuffle"]
[[[1, 2, 3]], [], [], []]
Output
[null, [3, 1, 2], [1, 2, 3], [1, 3, 2]]

Explanation
Solution solution = new Solution([1, 2, 3]);
solution.shuffle();    // Shuffle the array [1,2,3] and return its result.
// Any permutation of [1,2,3] must be equally likely to be returned.
// Example: return [3, 1, 2]
solution.reset();      // Resets the array back to its original configuration [1,2,3]. Return [1, 2, 3]
solution.shuffle();    // Returns the random shuffling of array [1,2,3]. Example: return [1, 3, 2]


## 3. Constraints

• 1 <= nums.length <= 200
• -106 <= nums[i] <= 106
• All the elements of nums are unique.
• At most 5 104 calls *in total will be made to reset and shuffle.

## 5. Solutions

class Solution {

int[] nums;
int[] shuffle;
Random random;

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

public int[] reset() {
return nums;
}

public int[] shuffle() {
shuffle = nums.clone();
for (int i = 0; i < shuffle.length; i++) {
swap(i, random.nextInt(shuffle.length));
}
return shuffle;
}

private void swap(int a, int b) {
int temp = shuffle[a];
shuffle[a] = shuffle[b];
shuffle[b] = temp;
}
}

/**
* 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();
*/