up09-6 (DFA emulator)

#include <iostream>
#include <string>
#include <map>
#include <set>
#include <utility>


namespace state_machine {
    struct StateMachine
    {
        std::string start_state;
        std::set<std::string> states;
        std::set<char> alphabet;
        std::set<std::string> end_states;
        std::map<std::pair<std::string, char>, std::string> functions;

        StateMachine(const std::set<std::string> &states = {},
                        const std::set<char> &alphabet = {},
                        const std::map<std::pair<std::string, char>, std::string> &functions = {},
                        const std::string &start_state = {},
                        const std::set<std::string> &end_states = {}
        ) : start_state(start_state),
            states(states),
            alphabet(alphabet),
            end_states(end_states),
            functions(functions) {}
    };

    std::tuple<bool, unsigned, std::string> is_word(const StateMachine &sm, const std::string &s)
    {
        auto curr_state = sm.start_state;
        for (size_t i = 0; i < s.size(); ++i) {
            auto tmp = sm.functions.find(std::pair<std::string, char>{curr_state, s[i]});
            if (tmp != sm.functions.end()) {
                curr_state = tmp->second;
            } else {
                return std::tuple(false, i, curr_state);
            }
        }

        return std::tuple(sm.end_states.find(curr_state) != sm.end_states.end(), s.size(), curr_state);
    }
}

int main()
{
    state_machine::StateMachine sm;
    char c;
    std::string curr, next;
    while (std::cin >> curr && curr != "END") {
        std::cin >> c >> next;
        sm.states.insert(curr);
        sm.states.insert(next);
        sm.alphabet.insert(c);
        sm.functions.insert({std::pair<std::string, char>(curr, c), next});
    }
    while (std::cin >> curr && curr != "END") {
        sm.end_states.insert(curr);
    }
    std::cin >> sm.start_state;

    std::string str;
    std::cin >> str;

    auto ans = state_machine::is_word(sm, str);
    std::cout << std::get<0>(ans) << std::endl << std::get<1>(ans) << std::endl << std::get<2>(ans) << std::endl;
}