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189_rotate.py
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189_rotate.py
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class Solution(object):
# 暴力旋转k次 O(n*k)
def rotate(self, nums, k):
"""
:type nums: List[int]
:type k: int
:rtype: None Do not return anything, modify nums in-place instead.
"""
while k:
temp = nums[-1]
for i in range(len(nums)-1, 0, -1):
nums[i] = nums[i-1]
nums[0] = temp
k -= 1
# 使用额外数组 O(n)+O(n)
def rotate_2(self, nums, k):
new_nums = [0]*len(nums)
for idx in range(len(nums)):
new_nums[(idx+k) % len(nums)] = nums[idx]
for i in range(len(nums)):
nums[i] = new_nums[i]
# 使用反转
def rotate_3(self, nums, k):
'''
假设 n=7 且 k=3
原始数组 : 1 2 3 4 5 6 7
反转所有数字后 : 7 6 5 4 3 2 1
反转前 k 个数字后 : 5 6 7 4 3 2 1
反转后 n-k 个数字后 : 5 6 7 1 2 3 4 --> 结果
'''
def reverse(nums, start, end):
while start < end:
nums[start], nums[end] = nums[end], nums[start]
start += 1
end -= 1
# 很关键,k可能会大于len(nums)
k %= len(nums)
reverse(nums, 0, len(nums)-1)
reverse(nums, 0, k-1)
reverse(nums, k, len(nums)-1)