back to switch :)

day23.cpp

@@ -13,37 +13,43 @@ using namespace intcode;
 
 namespace {
 
-using Packet = std::pair<ValueType, ValueType>;
-using Ethernet = std::deque<std::pair<std::size_t, Packet>>;
+struct Payload { ValueType x, y; };
+struct Packet { ValueType destination; Payload payload; };
+using Ethernet = std::deque<Packet>;
 
 auto BuildNetwork(Machine m) -> std::vector<Machine> {
-  auto& i = std::get<Input>(Step(m)).pos;
   std::vector<Machine> machines;
+  auto& i = std::get<Input>(Step(m)).pos;
   for (i = 0; i < 50; i++) {
     machines.push_back(m);
   }
   return machines;
 }
 
-auto Interact(Ethernet & ethernet, Machine & m, std::optional<Packet> p) -> void {
-  std::visit(overloaded{
-  [&](Input i) {
-    if (p) {
-      i.pos = p->first;
-      StepInput(m, p->second);
-      Interact(ethernet, m, {});
-    } else {
-      i.pos = -1; // no packet
+auto Interact(Ethernet & ethernet, Machine & m, std::optional<Payload> p) -> void {
+  for(;;) {
+    auto e = Step(m);
+    switch (e.index()) {
+      default: throw std::runtime_error{"unexpected halt"};
+      case 0: {
+        auto& i = std::get<0>(e).pos;
+        if (p) {
+          i = p->x;
+          StepInput(m, p->y);
+          p = {};
+          break;
+        }
+        i = -1; // no packet
+        return;
+      }
+      case 1: {
+        auto d = std::get<1>(e).val;
+        auto x = StepOutput(m);
+        auto y = StepOutput(m);
+        ethernet.push_back({d, {x,y}});
+      }
     }
-  },
-  [&](Output d) {
-    auto x = StepOutput(m);
-    auto y = StepOutput(m);
-    ethernet.push_back({d.val, {x,y}});
-    Interact(ethernet, m, p);
-  },
-  [](Halt) -> void { throw std::runtime_error{"unexpected halt"}; },
-  }, Step(m));
+  }
 }
 
 } // namespace
@@ -55,24 +61,24 @@ auto main() -> int {
 
   std::optional<ValueType> part1;
   std::optional<ValueType> part2;
-  std::optional<Packet> nat;
+  std::optional<Payload> nat;
 
   for(;;) {
     if (!ethernet.empty()) {
-      auto [dest, p] = ethernet.front();
+      auto packet = ethernet.front();
       ethernet.pop_front();
-      if (dest == 255) {
-        nat = p;
-        if (!part1) { part1 = p.second; }
+      if (packet.destination == 255) {
+        nat = packet.payload;
+        if (!part1) { part1 = packet.payload.y; }
       } else {
-        Interact(ethernet, machines.at(dest), p);
+        Interact(ethernet, machines.at(packet.destination), packet.payload);
       }
     } else if (nat) {
-      if (nat->second == part2) { break; }
-      part2 = nat->second;
+      if (part2 == nat->y) { break; }
+      part2 = nat->y;
       Interact(ethernet, machines[0], nat);
     } else {
-      for (auto && m : machines) {
+      for (auto & m : machines) {
         Interact(ethernet, m, {});
       }
     }