题解 | 大水题

#include <iostream>
using namespace std;

int weishu(int a){
    int sum = 0;
 while(a!=0){
    sum+=a%10;
    a/=10;
 }
 return sum;
}

int main() {
    long long n;
    int sum = 0;
    cin >> n;
    int count = weishu(n);
    while(count > 9){
    count = weishu(count);
    }
   
    cout << count << endl;
}

注意使用循环