leetcode 189. Rotate Array

class Solution {
public:
    void rotate(vector<int>& nums, int k) {
        int length = nums.size();
        if(length <= 1 || k <= 0)
            return;
        k = k%length;
        rotate_core(nums,0,length-1);
        rotate_core(nums,0,k-1);
        rotate_core(nums,k,length-1);
        return;
    }
    void rotate_core(vector<int>& nums,int start,int end){
        while(start < end){
            int tmp = nums[start];
            nums[start] = nums[end];
            nums[end] = tmp;
            start++;
            end--;
        }
        return;
    }
};