# Shuffle an Array

## Problem

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.

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]
```

Constraints:

- 1 <= nums.length <= 50
- -106 <= nums[i] <= 106
- All the elements of nums are unique.
- At most 104 calls in total will be made to reset and shuffle.

## Solution

Using the Fisher-Yates algorithm for an in-place shuffle.

I actually learned the Fisher-Yates algorithm via my Anki flashcards, so this was quite helpful!

```
class Solution {
int[] original;
public Solution(int[] nums) {
this.original = nums;
}
public int[] reset() {
return this.original;
}
public int[] shuffle() {
var r = new Random();
var copy = new int[this.original.length];
System.arraycopy(this.original, 0, copy, 0, this.original.length);
for (int i = copy.length - 1; i > 0; i--) {
var j = r.nextInt(i + 1);
var tmp = copy[i];
copy[i] = copy[j];
copy[j] = tmp;
}
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();
*/
```