_384_ShuffleanArray.java

package leetcode_1To300;

import java.util.Random;

/**
 * 本代码来自 Cspiration，由 @Cspiration 提供
 * 题目来源：http://leetcode.com
 * - Cspiration 致力于在 CS 领域内帮助中国人找到工作，让更多海外国人受益
 * - 现有课程：Leetcode Java 版本视频讲解（1-900题）（上）（中）（下）三部
 * - 算法基础知识（上）（下）两部；题型技巧讲解（上）（下）两部
 * - 节省刷题时间，效率提高2-3倍，初学者轻松一天10题，入门者轻松一天20题
 * - 讲师：Edward Shi
 * - 官方网站：https://cspiration.com
 * - 版权所有，转发请注明出处
 */
public class _384_ShuffleanArray {
    /**
     * 384. Shuffle an Array
     * // 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();

     time : O(n)
     * @param nums
     */

    private int[] nums;
    private Random rmd;

    // 题中第构造函数时Solution
    public _384_ShuffleanArray(int[] nums) {
        this.nums = nums;
        rmd = new Random();
    }

    /** Resets the array to its original configuration and return it. */
    public int[] reset() {
        return nums;
    }

    /** Returns a random shuffling of the array. */
    public int[] shuffle() {
        if (nums == null) return null;
        int[] clone = nums.clone();
        for (int i = 1; i < clone.length; i++) {
            int random = rmd.nextInt(i + 1);
            swap(clone, i, random);
        }
        return clone;
    }
    private void swap(int[] clone, int i, int j) {
        int temp = clone[i];
        clone[i] = clone[j];
        clone[j] = temp;
    }
}