Given an array, rotate the array to the right by k steps, where k is non-negative.

Example 1:

Input: [1,2,3,4,5,6,7] and k = 3
Output: [5,6,7,1,2,3,4]
Explanation:
rotate 1 steps to the right: [7,1,2,3,4,5,6]
rotate 2 steps to the right: [6,7,1,2,3,4,5]
rotate 3 steps to the right: [5,6,7,1,2,3,4]
Example 2:
Input: [-1,-100,3,99] and k = 2
Output: [3,99,-1,-100]
Explanation:
rotate 1 steps to the right: [99,-1,-100,3]
rotate 2 steps to the right: [3,99,-1,-100]
Note:
Try to come up as many solutions as you can, there are at least 3 different ways to solve this problem.
Could you do it in-place with O(1) extra space?

题意是将一个数组按照给定的数字截取反转,要求时间复杂度为O(1)。解题思路需要数组的移动,每次将最后一个元素取出来赋值到数组第一个元素位置。

实现

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# author: xwolf
# origin: https://leetcode.com/problems/rotate-array/description/
# date: 2018-08-10


class (object):

    def __init__(self):
        pass


    def roate(nums, k):
        """
        :param nums:
        :param k:
        :return:
        """
        c = len(nums) - k
        a = nums[0:c]
        b = nums[c:len(nums)]
        nums[0:k] = b
        nums[k:] = a
        return nums


if __name__ == '__main__':
    rate = RoateArray()
    a = [-1, -100, 3, 99]
    print(rate.roate(a, 2))

参考

• 189. Rotate Array