From c8470b2056c83faae0fa5de2bd50775f1d124f4e Mon Sep 17 00:00:00 2001
From: Eric Mertens <emertens@gmail.com>
Date: Sat, 5 Nov 2022 11:19:32 -0700
Subject: [PATCH] 23

---
 CMakeLists.txt |  3 ++
 day15.cpp      |  8 ++---
 day23.cpp      | 96 ++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 103 insertions(+), 4 deletions(-)
 create mode 100644 day23.cpp

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4801ba0..b9361eb 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -36,3 +36,6 @@ target_link_libraries(day13 intcode)
 
 add_executable(day15 day15.cpp)
 target_link_libraries(day15 intcode)
+
+add_executable(day23 day23.cpp)
+target_link_libraries(day23 intcode)
diff --git a/day15.cpp b/day15.cpp
index f47ba7a..386a452 100644
--- a/day15.cpp
+++ b/day15.cpp
@@ -15,7 +15,7 @@ namespace {
 using CoordOp = Coord(Coord);
 CoordOp* const moves[4] {Up, Down, Left, Right};
 
-auto Interact(Machine & m, ValueType cmd) {
+auto Interact(Machine & m, ValueType cmd) -> ValueType {
   std::get<Input>(Step(m)).pos = cmd;
   return std::get<Output>(Step(m)).val;
 }
@@ -54,7 +54,7 @@ auto Explore(Machine m) -> std::map<Coord, ValueType> {
 
 // Breadth first search of maze finding shortest path to origin
 // and furthest point in the maze from the airsource.
-auto Compute12(std::map<Coord, ValueType> world) -> std::pair<int, int> {
+auto Compute(std::map<Coord, ValueType> world) -> std::pair<int, int> {
   // Find starting coordinate and remove all the walls from the map
   Coord start {};
   for (auto it = world.begin(); it != world.end(); ) {
@@ -72,7 +72,7 @@ auto Compute12(std::map<Coord, ValueType> world) -> std::pair<int, int> {
        !todo.empty();
        todo.pop_front())
   {
-    auto && [steps, here] = todo.front();
+    auto [steps, here] = todo.front();
     if (Coord{0,0} == here) part1 = steps;
     part2 = steps;
 
@@ -89,7 +89,7 @@ auto Compute12(std::map<Coord, ValueType> world) -> std::pair<int, int> {
 } // namespace
 
 auto main() -> int {
-  auto [p1,p2] = Compute12(Explore(Machine{ParseStream(std::cin)}));
+  auto [p1,p2] = Compute(Explore(Machine{ParseStream(std::cin)}));
   std::cout << "Part 1: " << p1 << std::endl;
   std::cout << "Part 2: " << p2 << std::endl;
 }
diff --git a/day23.cpp b/day23.cpp
new file mode 100644
index 0000000..412ca6c
--- /dev/null
+++ b/day23.cpp
@@ -0,0 +1,96 @@
+#include <cstddef>
+#include <deque>
+#include <iostream>
+#include <stdexcept>
+#include <tuple>
+#include <utility>
+#include <variant>
+#include <vector>
+#include <fstream>
+
+#include <intcode/intcode.hpp>
+using namespace intcode;
+
+namespace {
+
+using Packet = std::pair<ValueType, ValueType>;
+using Ethernet = std::deque<std::pair<std::size_t, Packet>>;
+
+auto BuildNetwork(Machine m) -> std::vector<Machine> {
+  std::vector<Machine> machines;
+  for (int i = 0; i < 50; i++) {
+    machines.push_back(m);
+    std::get<Input>(Step(machines.back())).pos = i;
+  }
+  return machines;
+}
+
+auto Interact(Ethernet & ethernet, Machine & m, std::optional<Packet> p) -> void {
+  for(;;) {
+    auto effect = Step(m);
+    switch (effect.index()) {
+
+    default:
+      throw std::runtime_error{"unexpected halt"};
+
+    case 0: // Input
+      if (p) {
+        std::get<Input>(effect).pos = p->first;
+        std::get<Input>(Step(m)).pos = p->second;
+        p = {};
+        break;
+      }
+      std::get<Input>(effect).pos = -1; // no packet
+      return;
+
+    case 1: // Output
+      auto d = std::get<Output>(effect).val;
+      auto x = std::get<Output>(Step(m)).val;
+      auto y = std::get<Output>(Step(m)).val;
+      ethernet.push_back({d, {x,y}});
+      break;
+    }
+  }
+}
+
+} // namespace
+
+auto main(int argc, char ** argv) -> int {
+  if (2 != argc) { return 1; }
+  std::ifstream fin {argv[1]};
+
+  auto machines = BuildNetwork(Machine{ParseStream(fin)});
+  auto ethernet = Ethernet{};
+
+  std::optional<ValueType> part1;
+  std::optional<ValueType> part2;
+  std::optional<Packet> nat;
+
+  for(;;) {
+    if (ethernet.empty()) {
+      if (nat) {
+        if (nat->second == part2) { break; }
+        part2 = nat->second;
+        Interact(ethernet, machines[0], nat);
+      } else {
+        for (auto && m : machines) {
+          Interact(ethernet, m, {});
+        }
+      }
+    } else {
+      auto [dest, p] = ethernet.front();
+      ethernet.pop_front();
+      if (dest == 255) {
+        nat = p;
+        if (!part1) { part1 = p.second; }
+      } else if (dest < 50) {
+        Interact(ethernet, machines[dest], p);
+      } else {
+        throw std::runtime_error{"bad destination"};
+      }
+    }
+  }
+
+  std::cout << "Part 1: " << *part1 << std::endl;
+  std::cout << "Part 2: " << *part2 << std::endl;
+}