64. 求1+2+...+n
求1+2+3+...+n
http://www.nowcoder.com/questionTerminal/7a0da8fc483247ff8800059e12d7caf1
用短路法
如果a and b,a,b都不为0返回b,a为0返回a也就是0,a不为0b为0返回b也就是0
class Solution: def Sum_Solution(self, n): # write code here return n and n+self.Sum_Solution(n-1)