题解 | The Biggest Water Problem

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int m = one(n);
        System.out.println(m);
    }
    public static int one(int n){
        String s = String.valueOf(n);
        String[] str = s.split("");
        int m = 0;
        for(int i=0;i<str.length;i++){
            m += Integer.parseInt(str[i]);
        }
        if(m>=10){
            m = one(m);
        }
        return m;
    }
}