public class Solution {
    public int Sum_Solution(int n) {
       //方法一短路与
       /*
       int ans = n;
       boolean flag = (ans>0) && (ans+=Sum_Solution(n-1))>0;
       return ans;*/
       //方法二求数组个数
       int m = (int)Math.pow(n, 2)+n;
       return m>>1;
    }
}