bool check_board(list_type const& list, std::size_t level)
{
for(std::size_t i = 0 ;i < level; ++i){
if((list.at(i) == list.at(level))
|| (list.at(level) - list.at(i) == level - i)
|| (list.at(i) - list.at(level) == level - i))
return false;
}
return true;
}
void update_board(std::size_t pos, std::size_t val)
{
list_.at(pos) = val;
}
