template <>
struct std::hash<std::pair<int, int>>
{
static constexpr std::size_t size = sizeof(int) * 2;
using result_type = std::bitset<size * CHAR_BIT>;

result_type operator()(const std::pair<int, int>& val) const
{
result_type ret;
ret |= result_type(get<0>(val));
ret |= result_type(get<1>(val));
return ret;
}
};