Simple Python solution in one line Python string fundamental: string[start:end:step] start = -1 end = -(1+len(str)) step = -1

#
# 反转字符串
# @param str string字符串 
# @return string字符串
#
class Solution:
    def solve(self , str ):
        # write code here
        return str[-1:-(1+len(str)):-1]