题解 | #求1+2+3+...+n#

import java.util.*;
public class Solution {
    public int Sum_Solution(int n) {
        return recur(0, n);
    }

    int recur(int sum, int n) {
        if(n == 1) return sum + 1;
        return recur(sum + n, n - 1);
    }
}