384. 打乱数组

给你一个整数数组 nums，设计算法来打乱一个没有重复元素的数组。

实现 Solution class:

Solution(int[] nums) 使用整数数组 nums 初始化对象
int[] reset()重设数组到它的初始状态并返回
int[] shuffle()返回数组随机打乱后的结果

示例：

输入
["Solution", "shuffle", "reset", "shuffle"] [[[1, 2, 3]], [], [], []]
输出
[null, [3, 1, 2], [1, 2, 3], [1, 3, 2]]

解释

Solution solution = new Solution([1, 2, 3]);
solution.shuffle();    // 打乱数组 [1,2,3] 并返回结果。任何 [1,2,3]的排列返回的概率应该相同。例如，返回 [3, 1, 2]
solution.reset();      // 重设数组到它的初始状态 [1, 2, 3] 。返回 [1, 2, 3]
solution.shuffle();    // 随机返回数组 [1, 2, 3] 打乱后的结果。例如，返回 [1, 3, 2]

class Solution {
    private int[] nums;
    private Random random;
    public Solution(int[] nums) {
        this.nums = nums;
        random = new Random();
    }
    
    public int[] reset() {
        return nums;
    }
    
    public int[] shuffle() {
        if (nums == null)
            return null;
        int[] a = nums.clone();
        for (int j = 1; j < a.length; ++j) {
            int i = random.nextInt(j + 1);
            swap(a, i, j);
        }
        return a;
    }
    public void swap(int[] a, int i, int j) {
        int t = a[i];
        a[i] = a[j];
        a[j] = t;
    }
}

/**
 * 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();
 */