（LeetCode）Rotate Array --- 逆置数组

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

Credits:

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

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解题分析：

对于这个可以利用分治方法，可以利用给出的 k 值将数列分成两部分，

分别对其中的每一部分进行逆置，然后再把整个逆置一下。

实现逆置的算法原理：

a ^= b

b ^= a

a ^= b

# -*- coding:utf-8 -*-
__author__ = 'jiuzhang'
class Solution(object):
    def rotate(self, nums, k):
        n = len(nums)
        k %= n
        self.reverse(nums, 0, n - k)
        self.reverse(nums, n - k, n)
        self.reverse(nums, 0, n)
    def reverse(self, nums, start, end):
        for x in range(start, (start + end) / 2):
            nums[x] ^= nums[start + end - x - 1]
            nums[start + end - x - 1] ^= nums[x]
            nums[x] ^= nums[start + end - x - 1]