poj 2190 ISBN

//不要被这句话迷惑了：Each of the first nine digits can take a value between 0 and 9！！！无关的一句话
//这题需要考虑的情况比较多，只要细心一点分清楚需要讨论的情况就OK！ 
#include<iostream>
#include<string>
#include<algorithm>
using namespace std;

int main()
{
    string str;
    cin >> str;
    int i, j, pos, sum, ans;
    bool flag;
    pos = str.find('?');
    //如果？在字符串的结尾情况，在这情况之下又有两种情况：因为其结尾可以为X，也可以为其他的数字 
    if (pos == 9){
            sum = 0;
            flag = false;
            for (i = 0, j = 10; i < 9; i++, j--){
                sum += (str[i]-48)*j;
            }
            for (ans = 0; ans < 10; ans++){
                int tmp = sum;
                tmp += ans;
                if (tmp % 11 == 0){
                        flag = true;
                        break;
                }
            }
            if (flag)
               cout << ans << endl;
            else{
                 sum += 10;
                 if (sum % 11 == 0)
                     cout << "X" << endl;
                 else
                     cout << -1 << endl;
            }
    }
    // 如果？不在结尾的情况，也有两种情况讨论！ 
    else{
         if (str[9] == 'X'){
                    sum = 0;
                    flag = false;
                    for (i = 0, j = 10; i < 9; i++, j--){
                        if (str[i] == '?')  continue;
                        else   sum += (str[i]-48)*j;
                    }
                    sum += 10;
                    for (ans = 0; ans <= 9; ans++){
                        int tmp = sum;
                        tmp += ans * (10-pos);
                        if (tmp % 11 == 0){
                                flag = true;
                                break;
                        }
                    }
                    if (flag)
                       cout << ans << endl;
                    else
                       cout << "-1" << endl;
         }
         else{
              sum = 0;
              flag = false;
              for (i = 0, j = 10; i < 10; i++, j--){
                  if (str[i] == '?')  continue;
                  else   sum += (str[i]-48)*j;
              }
              for (ans = 0; ans <= 9; ans++){
                        int tmp = sum;
                        tmp += ans * (10-pos);
                        if (tmp % 11 == 0){
                                flag = true;
                                break;
                        }
                    }
                    if (flag)
                       cout << ans << endl;
                    else
                       cout << "-1" << endl;
         }
    }
    
    system("pause");
}
/*
020110331?
156881111?
?201103311
03?1103311
1
X
0
3 
*/