Separate out Dijkstra implementation

This separates the Dijkstra implementation into its own generic function.

Whilst doing this we can simplify the code and also save yet more memory!

Still don't get correct results for part 2.

2021/puzzle-23-01.cc

@@ -169,6 +169,18 @@ private:
 std::array<Type, 15> State::finished_ = {'.', '.', '.', '.', '.', '.', '.', 'A',
                                          'B', 'C', 'D', 'A', 'B', 'C', 'D'};
 
+std::ostream& operator<<(std::ostream& os, State const& s)
+{
+  os << "#############\n"
+     << '#' << s.node(0) << s.node(1) << '.' << s.node(2) << '.' << s.node(3) << '.' << s.node(4)
+     << '.' << s.node(5) << s.node(6) << "#\n"
+     << "###" << s.node(7) << '#' << s.node(8) << '#' << s.node(9) << '#' << s.node(10) << "###\n"
+     << "  #" << s.node(11) << '#' << s.node(12) << '#' << s.node(13) << '#' << s.node(14) << "#\n"
+     << "  #########\n";
+
+  return os;
+}
+
 struct StateTranstitionManager
 {
   bool is_finished(State const& state) { return state.finished(); }