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();
 */