384. Shuffle an Array

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Problem

Given an integer array nums, design an algorithm to randomly shuffle the array.

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]

Code

Fisher-Yates Shuffle

class Solution {
    private int[] nums;
    private Random rand;

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

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

    public int[] shuffle() {
        int[] clone = nums.clone();
        for(int end = nums.length - 1; end >= 0; end--){
            int randNum = rand.nextInt(end + 1);
            swap(clone, randNum, end);
        }
        return clone;
    }
    
    private void swap(int[] nums, int i, int j){
        int temp = nums[i];
        nums[i] = nums[j];
        nums[j] = temp;
    }
}