Leetcode 384: 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();


Below solution didn't pass AC but I believe the code works. I'm not sure how LC verifies whether it's random.

public class Solution {

    private int[] copy = null;
    private Random random = new Random();
    
    public Solution(int[] nums) {
        copy = nums;    
    }
    
    /** Resets the array to its original configuration and return it. */
    public int[] Reset() {
        return copy;
    }
    
    /** Returns a random shuffling of the array. */
    public int[] Shuffle() {
        var nums = new int[copy.Length];
        var result = new int[copy.Length];
        Array.Copy(copy, nums, copy.Length);;
        
        for (int i = 0; i < copy.Length; i++)
        {
            var ran = random.Next(i, copy.Length);
            
            result[i] = nums[ran];
            
            // to avoid the element at ran to be chosen again
            nums[ran] = nums[i];
        }
        
        return result;
    }
}

/**
 * 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();
 */