【LeetCode】189

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.[show hint]

Hint:Could you do it in-place with O(1) extra space?

Related problem: Reverse Words in a String II

Solution 1：reverse[1,2,3,4]=[4,3,2,1], reverse[5,6,7]=[7,6,5], reverse[4,3,2,1,7,6,5]=[5,6,7,1,2,3,4]

#include<algorithm>
class Solution {     
public:
    void rotate(vector<int>& nums, int k) {      //runtime:24ms
        int n=nums.size();
        k %= n;
        reverse(nums.begin(),nums.begin()+n-k);
        reverse(nums.begin()+n-k,nums.end());
        reverse(nums.begin(),nums.end());
    }
};

Solution 2：超时

class Solution {
public:
    void rotate(vector<int>& nums, int k) {
        int n=nums.size();
        k %= n;
        while(k--){
            int temp=nums[n-1];
            for(int i=n-1;i>0;i--){
                nums[i]=nums[i-1];
            }
            nums[0]=temp;
        }
    }
};

Solution 3:

void rotate(int nums[], int n, int k) {  
    k = k % n;  
    if (k == 0) return;  
    int *temp = new int[n];  
    memcpy(temp, nums+(n-k), sizeof(int)*k);  
    memcpy(temp+k, nums, sizeof(int)*(n-k));  
    memcpy(nums, temp, sizeof(int)*n);  
    delete[] temp;  
}