check

day02.cpp

@@ -10,7 +10,7 @@ namespace {
 auto Compute(Machine machine, ValueType x, ValueType y) {
   machine.At(1) = x;
   machine.At(2) = y;
-  machine.Step();
+  Step(machine);
   return machine.At(0);
 }
 

day05.cpp

@@ -18,7 +18,7 @@ auto Compute(Machine machine, ValueType d) -> ValueType {
       last_output = arg.val;
       return true;
     }},
-    machine.Step()));
+    Step(machine)));
   return last_output;
 }
 

day07.cpp

@@ -14,7 +14,7 @@ template <class R> auto Controller(Machine machine, R const &params) {
   std::vector<Machine> amps;
   for (auto p : params) {
     auto m = machine;
-    std::get<Input>(m.Step()).pos = p;
+    std::get<Input>(Step(m)).pos = p;
     amps.push_back(std::move(m));
   }
   return amps;
@@ -23,10 +23,10 @@ template <class R> auto Controller(Machine machine, R const &params) {
 template <class R>
 auto Feed(R &&amps, ValueType start) -> std::optional<ValueType> {
   for (auto &m : amps) {
-    auto i = m.Step();
+    auto i = Step(m);
     if (auto p = std::get_if<Input>(&i)) {
       p->pos = start;
-      start = std::get<Output>(m.Step()).val;
+      start = std::get<Output>(Step(m)).val;
     } else {
       return {};
     }

day09.cpp

@@ -18,7 +18,7 @@ auto Compute(Machine machine, ValueType d) -> ValueType {
       output = arg.val;
       return false;
     }},
-    machine.Step()));
+    Step(machine)));
   return output;
 }
 

day11.cpp

@@ -19,15 +19,15 @@ auto Compute(Machine machine, ValueType start)
   ValueType dy {-1};
 
   for (;;) {
-    auto effect = machine.Step();
+    auto effect = Step(machine);
 
     if (std::holds_alternative<Halt>(effect)) {
       return paint;
     }
 
     std::get<Input>(effect).pos = paint[here];
-    paint[here] = std::get<Output>(machine.Step()).val;
+    paint[here] = std::get<Output>(Step(machine)).val;
-    auto dir = std::get<Output>(machine.Step()).val;
+    auto dir = std::get<Output>(Step(machine)).val;
 
     std::swap(dx, dy);
     if (dir) {  

day13.cpp

@@ -15,13 +15,13 @@ auto Compute1(Machine machine)
   std::set<Coord> screen;
 
   for (;;) {
-    auto effect = machine.Step();
+    auto effect = Step(machine);
     if (std::holds_alternative<Halt>(effect)) {
       return screen.size();
     }
     auto x = std::get<Output>(effect).val;
-    auto y = std::get<Output>(machine.Step()).val;
+    auto y = std::get<Output>(Step(machine)).val;
-    auto v = std::get<Output>(machine.Step()).val;
+    auto v = std::get<Output>(Step(machine)).val;
 
     if (2 == v) { screen.insert({x,y}); } else { screen.erase({x,y}); }
   }
@@ -34,7 +34,7 @@ auto Compute2(Machine machine) {
 
   machine.At(0) = 2;
   for(;;) {
-    auto effect = machine.Step();
+    auto effect = Step(machine);
     if (std::holds_alternative<Halt>(effect)) {
       return score;
     } else if (auto i = std::get_if<Input>(&effect)) {
@@ -42,8 +42,8 @@ auto Compute2(Machine machine) {
              : paddleX > ballX ? -1 : 0;
     } else {
       auto x = std::get<Output>(effect).val;
-      auto y = std::get<Output>(machine.Step()).val;
+      auto y = std::get<Output>(Step(machine)).val;
-      auto v = std::get<Output>(machine.Step()).val;
+      auto v = std::get<Output>(Step(machine)).val;
 
       if (-1 == x && 0 == y) {
         score = v;

day15.cpp

@@ -4,6 +4,7 @@
 #include <tuple>
 #include <map>
 #include <deque>
+#include <vector>
 
 #include <intcode.hpp>
 using namespace intcode;
@@ -13,46 +14,65 @@ namespace {
 using Coord = std::pair<ValueType, ValueType>;
 
 auto Compute(Machine machine) -> std::pair<int,int> {
-  int part1 = 0;
-  int part2 = 0;
-
   Coord here {0,0};
-  std::map<Coord, ValueType> world;
+  std::map<Coord, ValueType> world {{{0,0},1}};
 
-  std::deque<std::tuple<int, Coord, Machine>> todo {{0, {0,0}, std::move(machine)}};
+  using State = std::tuple<Coord, Machine>;
 
-  auto action = [&world, &todo](Machine m, int steps, ValueType cmd, Coord coord) {
+  std::vector<State> layer {{{0,0}, std::move(machine)}};
+  std::vector<State> next_layer;
+  
+  auto action = [&](Machine m, ValueType cmd, Coord coord) {
     if (!world.contains(coord)) {
-      std::get<Input>(m.Step()).pos = cmd;
+      std::get<Input>(Step(m)).pos = cmd;
-      auto o = std::get<Output>(m.Step()).val;
+      auto o = std::get<Output>(Step(m)).val;
       world[coord] = o;
       if (o) {
-        todo.emplace_back(steps + 1, coord, std::move(m));
+        next_layer.emplace_back(coord, std::move(m));
       }
     }
   };
 
-  while (!todo.empty()) {
+  int part1 = 0;
-    auto [steps, here, machine] = todo.front();
+  while (!layer.empty()) {
-    auto [x,y] = here;
+    for (auto && s : layer) {
-    todo.pop_front();
+      auto& [loc, m] = s;
-    
+      if (2 == world[loc]) {
-    if (2 == world[here]) {
-      part1 = steps;
-      todo.clear();
         world.clear();
-      world[here] = 2;
+        world[loc] = 2;
-      steps = 0;
+        auto start = std::move(m);
-      part2 = 0;
+        layer.clear();
+        layer.push_back({loc, std::move(start)});
+        goto loop2;
+      }
+      auto [x,y] = loc;
+      action(m, 1, {x,y-1});
+      action(m, 2, {x,y+1});
+      action(m, 3, {x-1,y});
+      action(std::move(m), 4, {x+1,y});
+    }
+    layer = std::move(next_layer);
+    next_layer.clear();
+    part1++;
   }
-    part2 = std::max(part2, steps);
 
-    action(machine, steps, 1, {x,y-1});
+  
-    action(machine, steps, 2, {x,y+1});
+loop2:
-    action(machine, steps, 3, {x-1,y});
+  int part2 = 0;
-    action(std::move(machine), steps, 4, {x+1,y});
+  while (!layer.empty()) {
+    for (auto && s : layer) {
+      auto& [loc, m] = s;
+      auto [x,y] = loc;
+      action(m, 1, {x,y-1});
+      action(m, 2, {x,y+1});
+      action(m, 3, {x-1,y});
+      action(std::move(m), 4, {x+1,y});
     }
-  return {part1,part2};
+    layer = std::move(next_layer);
+    next_layer.clear();
+    part2++;
+  }
+  return {part1, part2-1};
 }
 
 } // namespace

lib/include/intcode.hpp

@@ -36,9 +36,6 @@ public:
   Machine();
   explicit Machine(std::vector<ValueType> ram);
 
-  /// Advance machine until next side effect
-  auto Step() -> std::variant<Input, Output, Halt>;
-
   /// Access memory at absolute address
   /// @param address
   /// @return reference to memory at given address
@@ -48,8 +45,14 @@ public:
   /// @param offset from base pointer
   /// @return reference to memory at given offset
   auto Rel(std::size_t offset) -> ValueType &;
+
+  auto Next() -> ValueType &;
+  auto Goto(std::size_t address) -> void;
+  auto Rebase(std::size_t offset) -> void;
 };
 
+auto Step(Machine & m) -> std::variant<Input, Output, Halt>;
+
 struct BadInstruction : public std::runtime_error {
   explicit BadInstruction(char const* what);
 };

lib/intcode.cpp

@@ -11,11 +11,35 @@ Machine::Machine() : rom_{}, ram_{}, pc_{0}, base_{0} {}
 Machine::Machine(std::vector<ValueType> ram)
     : rom_{ram}, ram_{}, pc_{0}, base_{0} {}
 
-namespace {
+auto Machine::At(std::size_t i) -> ValueType & {
-auto Ref(Machine & m, ValueType instruction, std::size_t k, ValueType p)
+  return i < rom_.size() ? rom_[i] : ram_[i];
-    -> ValueType & {
+}
-  auto &v = m.At(k);
+
-  switch (instruction / p % 10) {
+auto Machine::Rel(std::size_t i) -> ValueType & {
+  return At(base_ + i);
+}
+
+auto Machine::Rebase(std::size_t offset) -> void {
+  base_ += offset;
+}
+
+
+auto Machine::Next() -> ValueType & {
+  return At(pc_++);
+}
+
+auto Machine::Goto(std::size_t address) -> void {
+  pc_ = address;
+}
+
+auto Step(Machine & m) -> std::variant<Input, Output, Halt> {
+  for (;;) {
+    auto instruction = m.Next();
+    auto modes = instruction / 10;
+
+    auto arg = [&]() -> ValueType & {
+      auto &v = m.Next();
+      switch ((modes /= 10) % 10) {
       case 0:
         return m.At(v);
       case 1:
@@ -25,68 +49,65 @@ auto Ref(Machine & m, ValueType instruction, std::size_t k, ValueType p)
       default:
         throw BadInstruction{"invalid addressing mode"};
       }
-}
+    };
-}
-
-auto Machine::At(std::size_t i) -> ValueType & {
-  return i < rom_.size() ? rom_[i] : ram_[i];
-}
-
-auto Machine::Rel(std::size_t i) -> ValueType & {
-  return At(base_ + i);
-}
-
-auto Machine::Step() -> std::variant<Input, Output, Halt> {
-  for (;;) {
-    auto instruction = At(pc_);
-    auto a = [=]() -> auto & { return Ref(*this, instruction, pc_+1, 100); };
-    auto b = [=]() -> auto & { return Ref(*this, instruction, pc_+2, 1000); };
-    auto c = [=]() -> auto & { return Ref(*this, instruction, pc_+3, 10000); };
 
     switch (instruction % 100) {
-    case 1:
+    case 1: {
-      c() = a() + b();
+      auto a = arg();
-      pc_ += 4;
+      auto b = arg();
+      auto& c = arg();
+      c = a + b;
       break;
+    }
 
-    case 2:
+    case 2: {
-      c() = a() * b();
+      auto a = arg();
-      pc_ += 4;
+      auto b = arg();
+      auto& c = arg();
+      c = a * b;
       break;
+    }
 
     case 3: {
-      auto &pos = a();
+      return Input{arg()};
-      pc_ += 2;
-      return Input{pos};
     }
 
     case 4: {
-      auto val = a();
+      return Output{arg()};
-      pc_ += 2;
-      return Output{val};
     }
 
-    case 5:
+    case 5: {
-      pc_ = a() ? b() : pc_ + 3;
+      auto a = arg();
+      auto b = arg();
+      if (a) { m.Goto(b); }
       break;
+    }
 
-    case 6:
+    case 6: {
-      pc_ = a() ? pc_ + 3 : b();
+      auto a = arg();
+      auto b = arg();
+      if (!a) { m.Goto(b); }
       break;
+    }
 
-    case 7:
+    case 7: {
-      c() = a() < b();
+      auto a = arg();
-      pc_ += 4;
+      auto b = arg();
+      auto& c = arg();
+      c = a < b;
       break;
+    }
 
-    case 8:
+    case 8: {
-      c() = a() == b();
+      auto a = arg();
-      pc_ += 4;
+      auto b = arg();
+      auto& c = arg();
+      c = a == b;
       break;
+    }
 
     case 9:
-      base_ += a();
+      m.Rebase(arg());
-      pc_ += 2;
       break;
 
     case 99: