In file included from /in/Compile/check.cpp:7:
/in/sokoban.hpp:143:58: error: implicit conversion changes signedness: 'int' to 'std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::size_type' (aka 'unsigned long') [-Werror,-Wsign-conversion]
        return static_cast<Cell>(state_str_[row * n_cols + col]);
                                 ~~~~~~~~~~ ~~~~~~~~~~~~~^~~~~
/in/sokoban.hpp:324:10: error: private field 'has_solution_' is not used [-Werror,-Wunused-private-field]
    bool has_solution_;
         ^
2 errors generated.
/in/Compile/Makefile:16: recipe for target 'main' failed
make: *** [main] Error 1