解法一:递归

class Solution {
public:
    int getSum(int n) {
        int res=n;
        n>0 && (res+=getSum(n-1));
        return res;
    }
};

解法二:公式法

class Solution {
public:
    int getSum(int n) {
        return (long long)n*(1+n)/2;
    }
};