Day 2, Part 2

#include <fstream>
#include <algorithm>
#include <cstring>
using namespace std;

ifstream fin ("data.in");
ofstream fout ("data.out");

char s[300][300];
int d[500], k;
long long dubl, tripl;

int la_fel(char a[], char b[]){
    int cont = 0;
    for(int i = 0; a[i] != 0; i++){
        if(a[i] != b[i]){
            cont++;
            if(cont == 2){
                return 0;
            }
        }
    }
    return 1;
}

void afis(char a[], char b[]){
    for(int i = 0; a[i] != 0; i++){
        if(a[i] == b[i]){
            fout<<a[i];
        }
    }
}

int main()
{
    while(fin>>s[k]){
        k++;
    }
    for(int i = 0; i < k; i++){
        for(int j = i + 1; j < k; j++){
            if(la_fel(s[i], s[j])){
                afis(s[i], s[j]);
            }
        }
    }
    return 0;
}