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.

[show hint]

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

Related problem: Reverse Words in a String II

三次reverse: 时间复杂度O(n), 空间复杂度O(1)

reverse(nums, 0, length - k - 1)

reverse(nums, length - k, length - 1)

reverse(nums, 0, length - 1)

这里还用到一个trick，交换变量不用额外空间：

a = a ^ b

b = a ^ b

a = a ^ b

使用异或避免溢出

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

　　public void reverse(int[] nums, int i, int j) {
　　　　while (i < j) {
　　　　　　nums[i] ^= nums[j];
　　　　　　nums[j] = nums[i] ^ nums[j];
　　　　　　nums[i] = nums[i] ^ nums[j];
　　　　　　i++;
　　　　　　j--;
　　　　}
　　}
}