AcWing每日一题--ISBN号码

https://www.acwing.com/problem/content/435/

#include<iostream>
using namespace std;
int main(void){
    string s;
    cin>>s;
    int res=0;
    for(int i=0,j=1;i<s.length()-1;i++){
        if(s[i]>='0'&&s[i]<='9')
            res+=j * (s[i]-'0'), j++;
    }
    res %= 11;
    char c='X';
    if(res<10) c=char(res+'0');

    if(s.back()==c) puts("Right");
    else{
        s.back()=c;
        cout<<s;
    }
    return 0;
}