【LeetCode】Rotate Array

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。