0384.打乱数组.java

import java.util.Arrays;
import java.util.Random;

/*
 * @lc app=leetcode.cn id=384 lang=java
 *
 * [384] 打乱数组
 *
 * https://leetcode.cn/problems/shuffle-an-array/description/
 *
 * algorithms
 * Medium (61.17%)
 * Likes:    283
 * Dislikes: 0
 * Total Accepted:    102.3K
 * Total Submissions: 167.2K
 * Testcase Example:  '["Solution","shuffle","reset","shuffle"]\n[[[1,2,3]],[],[],[]]'
 *
 * 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。打乱后，数组的所有排列应该是 等可能 的。
 * 
 * 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 1：
 * 
 * 
 * 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]
 * 
 * 
 * 
 * 
 * 提示：
 * 
 * 
 * 1 <= nums.length <= 50
 * -10^6 <= nums[i] <= 10^6
 * nums 中的所有元素都是 唯一的
 * 最多可以调用 10^4 次 reset 和 shuffle
 * 
 * 
 */

// @lc code=start
class Solution {
    private final int[] nums;
    private final int[] copy;
    private final Random random;

    public Solution(int[] nums) {
        this.nums = nums;
        this.random = new Random();
        this.copy = Arrays.copyOf(nums, nums.length);
    }

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

    public int[] shuffle() {
        for (int i = copy.length - 1; i >= 0; --i) {
            int n = random.nextInt(i + 1);
            int v = copy[i];
            copy[i] = copy[n];
            copy[n] = v;
        }

        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();
 */
// @lc code=end