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.
Credits:
Special thanks to @Freezen for adding this problem and creating all test cases.
AC代码：（Python）
class Solution:
# @param nums, a list of integer
# @param k, num of steps
# @return nothing, please modify the nums list in-place.
def rotate(self, nums, k):
n = len(nums)
k = k % n
nums[:] = nums[n-k:] + nums[:n-k]
要注意一个问题：
A little important thing to be cautious:
nums[:] = nums[n-k:] + nums[:n-k]
can't be written as:
nums = nums[n-k:] + nums[:n-k]
on the OJ.
The previous one can truly change the value of old nums, but the following one just changes its reference to a new nums not the value of old nums.
因为题目要求的是：
@return nothing, please modify the nums list in-place. 类似的还有：
def purify(lsst):
lst = lsst[:]
for num in lsst:
if num % 2 == 1:
lst.remove(num)
return lst
这是清除 list 中的奇数，要求不要在原输入上直接修改。
注意第二行不能 写成：
lst = lsst 而应该是：
lst = lsst[:] 这样才是值相同的两个list, 否则 lst = lsst 只是一个 list 的两个引用。 值 和 引用 的问题当属 Python 里的第一大坑。