题解 | The Biggest Water Problem

#include <stdio.h>

int main() {
    long int n;
    long int sum = 0;//第一次判断
    long int sum1 = 0;//第二次
    long int sum2 = 0;//特殊情况(数较大时)
    scanf("%ld", &n);//输入整数

    while (n != 0)//第一次变
    {
        long int a = n % 10;
        sum += a;
        n /= 10;
    }

    if (sum < 10)
    {
        printf("%ld\n", sum);
    }

    else //继续变身
    {
        while (sum != 0)
        {
        long int c = sum % 10;
        sum1 += c;
        sum /= 10;
        }
        if (sum1 >= 10)
        {
            while (sum1 != 0)
            {
            long int a = sum1 % 10;
            sum2 += a;
            sum1 /= 10;
            }
            printf("%ld\n", sum2);
        }
        else
        {
            printf("%ld\n", sum1);
        }
    }

    return 0;
}