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]

Related problem: Reverse Words in a String II

Credits:
Special thanks to @Freezen for adding this problem and creating all test cases.

思路: 三次反转，1：反转前部分，2：反转后部分，3：整个反转。

public class Solution {  
    void reverse(int[] nums, int start, int end) {  
        while(start < end) {  
            int temp = nums[start];  
            nums[start] = nums[end];  
            nums[end] = temp;  
            ++start;  
            --end;  
        }  
    }  
    public void rotate(int[] nums, int k) {  
        k = k % nums.length;  
        reverse(nums, 0, nums.length - 1 );  
        reverse(nums, 0, k - 1 );  
        reverse(nums, k, nums.length - 1 );  
    }  
}  

public class Solution {    
    public void rotate(int[] nums, int k) {  
        if(nums == null || nums.length <= 1) return;
        
        int[] buf = new int[k];
        int len = nums.length;
        int shifts = k % len;

        System.arraycopy(nums, len-shifts, buf, 0, shifts);
        System.arraycopy(nums, 0, nums, shifts, len-shifts);
        System.arraycopy(buf, 0, nums, 0, shifts);
    }  
}  

public class Solution {    
    public void rotate(int[] nums, int k) {
        if(k==0 || nums.length==k)
            return;
        k = k % nums.length;
        reverse(nums, 0, nums.length-k-1);
        reverse(nums, nums.length-k, nums.length-1);
        reverse(nums, 0, nums.length-1);
    }
    
    public void reverse(int[] nums, int left, int right){
        while(left < right){
            int temp = nums[left];
            nums[left] = nums[right];
            nums[right] = temp;
            left++;
            right--;
        }
    }
}