左旋转字符串

 1 # -*- coding:utf-8 -*-
 2 class Solution:
 3     def LeftRotateString(self, s, n):
 4         # write code here
 5         ss = ‘‘
 6         if len(s)==0 or n<0 or n>len(s):
 7             return ss
 8         if n==0 or n==len(s):
 9             return s
10         ss = s[n:]+s[0:n]
11         return ss

 1 # -*- coding:utf-8 -*-
 2 class Solution:
 3     def LeftRotateString(self, s, n):
 4         # write code here
 5         # 使用翻转
 6         if len(s) == 0 or n > len(s):
 7             return ‘‘
 8         if n == 0 or n == len(s):
 9             return s
10         s = self.reverse(s, 0, n - 1)
11         s = self.reverse(s, n, len(s) - 1)
12         s = self.reverse(s, 0, len(s) - 1)
13         return ‘‘.join(s)
14 
15     def reverse(self, s, start, end):
16         s = list(s)
17         while start < end:
18             temp = s[start]
19             s[start] = s[end]
20             s[end] = temp
21             start += 1
22             end -= 1
23         return s