链接：https://leetcode-cn.com/problems/qiu-12n-lcof/
class Solution { public: int sumNums(int n) { int res = n; n > 0 && (res += sumNums(n - 1)); return res; } };
剑指OFFER----面试题64. 求1+2+…+n
原文：https://www.cnblogs.com/clown9804/p/12496966.html
