再水一道题

#include <iostream> 
#include <cstring> // use strlen 
#include <string> 
using namespace std; 
const int Max = 1e2+50;

int main() { 
    char a[Max], b[Max], c[Max];
    char key[Max] = {}, tkey[Max] = {};  
    int fl = 0, sum = 26; 
    cin >> a >> b >> c; 
    for (int i = 0; i < strlen(a); ++i) {  
        if (key[a[i]-'A'] != '' && key[a[i]-'A'] != b[i]) { 
            fl = 1; 
            break; 
        }    
        else { 
            if (tkey[b[i]-'A'] != '' && tkey[b[i]-'A'] != a[i]) {
                fl = 1;  
                break; 
            }
            if (tkey[b[i]-'A'] == '') --sum; 
            key[a[i]-'A'] = b[i];     
            tkey[b[i]-'A'] = a[i]; 
        }
    }
    if (sum) 
        fl = 1; 
    if (fl) 
        cout << "Failed";
    else 
        for (int i = 0; i < strlen(c); ++i) 
            cout << key[c[i]-'A'];
    return 0; 
}

https://www.luogu.org/problemnew/show/P1071