Given an array, rotate the array to the right by k steps, where k is non-negative.

Example 1:

Input: [1,2,3,4,5,6,7] and k = 3
Output: [5,6,7,1,2,3,4]
Explanation:
rotate 1 steps to the right: [7,1,2,3,4,5,6]
rotate 2 steps to the right: [6,7,1,2,3,4,5]
rotate 3 steps to the right: [5,6,7,1,2,3,4]
 

Example 2:

Input: [-1,-100,3,99] and k = 2
Output: [3,99,-1,-100]
Explanation: 
rotate 1 steps to the right: [99,-1,-100,3]
rotate 2 steps to the right: [3,99,-1,-100]

Note:

• Try to come up as many solutions as you can, there are at least 3 different ways to solve this problem.
• Could you do it in-place with O(1) extra space?

題目解析 

思路:1 找到中心點
         2.將中心點左邊資料反轉(不包括中心點)
         3.將中心點右邊資料反轉(包括中心點)
          4. 將反轉後的資料合併
          5.合併後的資料反轉即可得到答案
        時間複雜度為o(n) 空間複雜度為o(1)

class Solution {
    public void rotate(int[] nums, int k) {
        int length = nums.length;
         k = k%length;
        if(length==1)
            return;
        if(k==0)
            return;
        
        reversal(nums,0,length-k-1);
        reversal(nums,length-k,length-1);
        reversal(nums,0,length-1);
    }
    public static void reversal(int[] nums,int i,int j){
        int t = 0;
      while (i < j && i >= 0) {

			t = nums[i];

			nums[i] = nums[j];

			nums[j] = t;

			i++;

			j--;

		}
    }
}