leetcode 189. Rotate Array

Rotate an array of n elements to the right by k steps.

For example, with n = 7 and k = 3, the array [1,2,3,4,5,6,7] is rotated to [5,6,7,1,2,3,4].

Note:
Try to come up as many solutions as you can, there are at least 3 different ways to solve this problem.

第一種方法：拼數組

class Solution {
public:
    void rotate(vector<int>& nums, int k) {
        if(nums.size() < 1) return;
        k = k % nums.size();
        vector<int> numm(nums.begin(), nums.begin()+nums.size()-k);
        vector<int> numk(nums.begin()+nums.size()-k, nums.end());
        for(int i=0; i < nums.size();i++){
            if(i < k){
                nums[i] = numk[i];
            }else{
                nums[i] = numm[i-k];
            }
        }
    }
};

第二種方法：兩次翻轉

class Solution {
public:
    void rotate(vector<int>& nums, int k) {
        if(nums.size() < 1) return;
        k = k % nums.size();
        int i = 0, j = nums.size()-1;
        while(i < j) swap(nums[i++], nums[j--]);
        i = 0; j = k-1;
        while(i < j) swap(nums[i++], nums[j--]);
        i = k; j = nums.size()-1;
        while(i < j) swap(nums[i++], nums[j--]);
    }
};

第三種方法：依次交換元素