求1+2+3+...+n
求1+2+3+...+n
http://www.nowcoder.com/questionTerminal/7a0da8fc483247ff8800059e12d7caf1
一行代码简便解法，直接递归短路代替if语句，当n为0或者负数时，自动忽略之后的递归
# -*- coding:utf-8 -*-
class Solution:
def Sum_Solution(self, n):
# write code here
return n and ( n + self.Sum_Solution(n-1) )