[Leetcode]384. Shuffle an Array

题目[leetcode链接]
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();

思路：
随机洗牌问题

从头开始遍历，每次在[0,len)之间产生一个随机数，交换遍历到的位置与随机数位置上的数。

具体代码实现：

public class Solution {    int[] nums;    int[] result;    public Solution(int[] nums) {        int len = nums.length;        this.nums = new int[len];        result = new int[len];        for (int i = 0; i < len; i++) {            this.nums[i] = nums[i];            result[i] = nums[i];        }    }    /*  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() {        int nums_len = nums.length;        Random random = new Random();        for (int i = 0; i < nums_len; i++) {            int r = random.nextInt(nums_len);            int temp = result[i];            result[i] = result[r];            result[r] = temp;        }        return result;    }}

需要注意的问题：

返回值result的创建不能在shuffle()函数中创建，这样每次shuffle都会新创建空间，浪费很多空间，应该如代码中写的 在类中创建一个成员变量，每次用都用这个就可以。