剑指offer-左旋转字符串-超简单解法
左旋转字符串
http://www.nowcoder.com/questionTerminal/12d959b108cb42b1ab72cef4d36af5ec
简单易懂的解法：
把两个s拼起来，然后从第n%len(s)开始取出len(s)个元素，就可以了
class Solution:
def LeftRotateString(self, s, n):
# write code here
if s == None or s == "":
return ""
len_s = len(s)
s = s + s
n = n%len_s
return s[n:n+len_s]