# LeetCode - 0189. Rotate Array
### 題目網址：https://leetcode.com/problems/rotate-array/
###### tags: `LeetCode` `Medium`

/*
    -LeetCode format-
    Problem: 189. Rotate Array
    Difficulty: Medium
    
    by Inversionpeter
*/



class Solution {
    
    int GCD(int a, int b) {
        int buffer;
        while (b)
            buffer = a, a = b, b = buffer % b;
        return a;
    }
    
public:
    void rotate(vector<int>& nums, int k) {
        k %= nums.size();
        if (!k)
            return;
        int groups = GCD(nums.size(), k), groupSize = nums.size() / groups;
        for (int i = 0, now = 0; i < groups; ++i, now = i) {
            for (int j = 1; j < groupSize; ++j) {
                if ((now += k) >= nums.size())
                    now -= nums.size();
                swap(nums[i], nums[now]);
            }
        }
    }
};