LeetCode 384. Shuffle an Array

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();

题目大意：实现洗牌算法。给定一个没有重复元素的数组，写shuffle和set函数，shuffle函数要求对nums数组进行洗牌然后返回，set函数要求返回原来的nums数组～
分析：设立两个数组nums和origin，如果set就返回不会更改的origin数组，如果要洗牌，从nums的最后一位开始，设index为0～n-1中的一个随机数，产生后将index与最后一位元素进行交换，这样最后一位就算敲定了，然后再往前一位，假设当前位的下标是k，那就产生0～k之间的一个随机数，然后交换，以此类推，rand() % (i + 1)表示生成0～i中的一个随机数～直到第一位为止～

class Solution {private:    vector<int> nums;    vector<int> origin;public:    Solution(vector<int> nums) {        this->nums = nums;        this->origin = nums;    }        /** Resets the array to its original configuration and return it. */    vector<int> reset() {        return origin;    }        /** Returns a random shuffling of the array. */    vector<int> shuffle() {        int n = nums.size();        for(int i = n - 1; i >= 0; i--) {            int index = rand() % (i + 1);            swap(nums[i], nums[index]);        }        return nums;    }};/** * Your Solution object will be instantiated and called as such: * Solution obj = new Solution(nums); * vector<int> param_1 = obj.reset(); * vector<int> param_2 = obj.shuffle(); */