753. Cracking the Safe

//https://leetcode.com/problems/cracking-the-safe/description/

#include <iostream>
#include <string>
#include <set>

using namespace std;

class Solution {
private:
    string sequence;
    set<string> passwords;
    int cursor;

    void addPassword(string pswd, int digit_limit) {
        if (passwords.find(pswd) == passwords.end()) {
            sequence += pswd;

            int pswd_len = (int)pswd.length();
            int seq_len = (int)sequence.length();
            if (seq_len > pswd_len) {
                while (cursor < seq_len - pswd_len) {
                    string ps = sequence.substr(cursor, pswd_len);
                    passwords.insert(ps);
                    cursor++;
                }
            }
        }
    }

    void backtrack(string &pswd, int num_digits, int digit_limit){
        if (num_digits == 0) {
            cout << "pswd: " << pswd << endl;
            addPassword(pswd, digit_limit);
            return;
        }

        for (int digit = 0; digit < digit_limit; digit++) {
            pswd += ('0' + digit);
            backtrack(pswd, num_digits - 1, digit_limit);
            pswd.pop_back();
        }
    }

public:
    Solution() {
        sequence = "";
        cursor = 0;
    }

    string crackSafe(int num_digits, int digit_limit) {
        string pswd = "";
        backtrack(pswd, num_digits, digit_limit);

        return sequence;
    }
};

int main(int argc, const char * argv[]) {
    Solution sol;
    cout << sol.crackSafe(2, 2) << endl;

    return 0;
}