up07-4 (MT)

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

int main()
{
    std::map<std::pair<char, char>, std::tuple<char, char, short int>> rules
            {
                    {std::pair{'S', '0'}, std::tuple{'S', '0', 1}},
                    {std::pair{'S', '1'}, std::tuple{'A', '1', 1}},
                    {std::pair{'S', '#'}, std::tuple{'S', '#', 1}},
                    {std::pair{'A', '0'}, std::tuple{'A', '0', 1}},
                    {std::pair{'A', '1'}, std::tuple{'S', '1', 1}},
                    {std::pair{'A', '#'}, std::tuple{'B', '#', -1}},
                    {std::pair{'B', '0'}, std::tuple{'B', '0', -1}},
                    {std::pair{'B', '1'}, std::tuple{'B', '1', -1}},
                    {std::pair{'B', '#'}, std::tuple{'C', '#', 1}},
                    {std::pair{'C', '0'}, std::tuple{'C', '0', 1}},
                    {std::pair{'C', '1'}, std::tuple{'D', '0', 0}},
                    {std::pair{'D', '0'}, std::tuple{'D', '0', 0}},
            };
    std::string s;
    while (std::cin >> s) {
        char state = 'S';
        long long int pos = 0;
        while (pos >= 0 && size_t(pos) < s.size()) {
            std::tuple tmp = rules[{state, s[pos]}];
            if (s[pos] == std::get<1>(tmp) && std::get<2>(tmp) == 0 && state == std::get<0>(tmp)) {
                break;
            }
            s[pos] = std::get<1>(tmp);
            pos += std::get<2>(tmp);
            state = std::get<0>(tmp);
        }
        std::cout << s << std::endl;
    }
}