Роман и Тошибки

#include <set>
#include <fstream>

using namespace std;

int main() {
    ifstream cin("broken-keyboard.in");
    ofstream cout("broken-keyboard.out");
    set<string> words;
    int n;
    cin >> n;
    for (int i = 0; i < n; ++i) {
        set<char> usedSymbolsInWord;
        string s;
        cin >> s;
        bool flag = false;
        string pref;
        for (unsigned int j = 0; j < s.length(); ++j) {
            if (usedSymbolsInWord.count(s[j]) != 0) {
                if (words.count(pref) == 0) {
                    for (unsigned int k = j; k < s.length(); ++k) {
                        words.insert(pref + s[k]);
                        pref += s[k];
                    }
                    flag = true;
                    break;
                } else {
                    break;
                }
            } else if (words.count(pref + s[j]) == 0) {
                for (unsigned int k = j; k < s.length(); ++k) {
                    words.insert(pref + s[k]);
                    pref += s[k];
                }
                flag = true;
                break;
            }
            usedSymbolsInWord.insert(s[j]);
            pref += s[j];
        }
        if (flag) {
            cout << "YES\n";
        } else {
            cout << "NO\n";
        }
    }
    return 0;
}