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.

解題思路：
這題考點陣列的運用。
這題在暑假面試的時候是卷子裡的題，當時解法太幼稚了。。。
普通的做法就是建立一個輔助旋轉的新陣列，將陣列旋轉好後又放回原陣列中。

好的做法（就地旋轉，額外空間使用為 O(1)）是：
1. 將陣列拆分為兩部分，一部分是挪到陣列前面的，另一部分是挪到陣列後面的部分
2. 分別將兩個部分各自的元素做逆置
3. 再對全部陣列元素做逆置
舉例：
1. Divide the array two parts: 1,2,3,4 and 5, 6
2. Rotate first part: 4,3,2,1,5,6
3. Rotate second part: 4,3,2,1,6,5
4. Rotate the whole array: 5,6,1,2,3,4

程式碼實現：

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

33 / 33 test cases passed.
Status: Accepted
Runtime: 1 ms