Решение задачи Головоломка с Acmp

#include <iostream>
#include <string>
#include <fstream>
#include <algorithm>
using namespace std;
 
int main()
{
    string t, rebus, words;
    int n, m, pos;
    ifstream fin("input.txt");
    fin >> n >> m;
    for(int i = 0; i < n; ++i) {
        fin >> t;
        rebus += t;
    }
    for(int i = 0; i < m; ++i) {
        fin >> t;
        words += t;
    }
    for(int i = 0; i < words.size(); ++i) {
        pos = rebus.find(words[i]);
        rebus.erase(pos, 1);
    }
    sort(rebus.begin(), rebus.end());
    cout << rebus;
    return 0;
}

n, m = map(int, input().split())
dict = {}
for i in range(n):
    str = input()
    for c in str:
        if c in dict:
            dict[c] += 1
        else:
            dict[c] = 1
for i in range(m):
    str = input()
    for c in str:
        dict[c] -= 1
for i in dict:
    for j in range(dict[i]):
        print(i, end="")