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代碼：（Python）

1 class Solution:2     # @param nums, a list of integer3     # @param k, num of steps4     # @return nothing, please modify the nums list in-place.5     def rotate(self, nums, k):6         n = len(nums)7         k = k % n8         nums[:] = nums[n-k:] + nums[:n-k]9         

要注意一個(gè)問(wèn)題：

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?yàn)轭}目要求的是：

@return nothing, please modify the nums list in-place.

類似的還有：

1 def purify(lsst):2     lst = lsst[:]3     for num in lsst:4         if num % 2 == 1:5             lst.remove(num)6     return lst

這是清除 list 中的奇數(shù)，要求不要在原輸入上直接修改。

注意第二行不能 寫(xiě)成：

lst = lsst

而應(yīng)該是：

lst = lsst[:]


這樣才是值相同的兩個(gè)list, 否則 lst = lsst 只是一個(gè) list 的兩個(gè)引用。


值 和 引用 的問(wèn)題當(dāng)屬 Python 里的第一大坑。