题解 | 求1+2+3+...+n

class Sum {
  public:
    Sum() {
        _ret += _i;
        ++_i;
    }
    static int GetRet() {
        return _ret;
    }
  private:
    static int _i;
    static int _ret;
};
int Sum::_i = 1;
int Sum::_ret = 0;
class Solution {
  public:
    int Sum_Solution(int n) {
// 变⻓数组
        Sum arr[n];
        return Sum::GetRet();
    }
};