3

CMakeLists.txt

@@ -23,6 +23,9 @@ target_link_libraries(day01 aocpp)
 add_executable(day02 day02.cpp)
 target_link_libraries(day02 aocpp intcode)
 
+add_executable(day03 day03.cpp)
+target_link_libraries(day03 aocpp)
+
 add_executable(day05 day05.cpp)
 target_link_libraries(day05 aocpp intcode)
 

day03.cpp

@@ -0,0 +1,93 @@
+#include <algorithm>
+#include <cstdint>
+#include <iostream>
+#include <fstream>
+#include <iterator>
+#include <vector>
+#include <map>
+#include <tuple>
+#include <string>
+
+#include <aocpp/Coord.hpp>
+#include <aocpp/Startup.hpp>
+using namespace aocpp;
+
+namespace {
+
+auto BuildLine(std::string instructions) -> std::vector<Coord>
+{
+  Coord here {};
+  std::vector<Coord> wire;
+
+  auto it = std::begin(instructions);
+  auto end = std::end(instructions);
+  while (it != end) {
+    auto start = it;
+    it = std::find(it, end, ',');
+    if (start == it) { throw std::runtime_error{"null command"}; }
+
+    Coord (*step)(Coord);
+    switch (*start++) {
+      case 'U': step = Up;    break;
+      case 'D': step = Down;  break;
+      case 'L': step = Left;  break;
+      case 'R': step = Right; break;
+      default: throw std::runtime_error{"bad command letter"};
+    }
+
+    auto n = std::stol(std::string{start, it});
+    for (int i = 0; i < n; i++) {
+      here = step(here);
+      wire.push_back(here);
+    }
+
+    // skip over comma
+    if (it != end) it++;
+  }
+  return wire;
+}
+
+struct Entry { bool w0, w1; std::int64_t part2; };
+
+auto Record (
+  std::map<Coord, Entry> & m,
+  bool Entry::* which,
+  std::vector<Coord> const& wire
+) -> void {
+  for (std::size_t i = 0; i < wire.size(); i++) {
+    auto & entry = m[wire[i]];
+    if (!(entry.*which)) {
+      entry.*which = true;
+      entry.part2 += i+1;
+    }
+  }
+}
+
+} // namespace
+
+auto main(int argc, char** argv) -> int {
+  auto fin = aocpp::Startup(argc, argv);
+
+  std::string line;
+  std::getline(fin, line);
+  auto wire0 = BuildLine(line);
+  std::getline(fin, line);
+  auto wire1 = BuildLine(line);
+
+  std::map<Coord, Entry> counts;
+  Record(counts, &Entry::w0, wire0);
+  Record(counts, &Entry::w1, wire1);
+
+  std::int64_t part1 = std::numeric_limits<std::int64_t>::max();
+  std::int64_t part2 = std::numeric_limits<std::int64_t>::max();
+
+  for (auto & [k,v] : counts) {
+    if (v.w0 && v.w1) {
+      part1 = std::min(part1, Norm1(k));
+      part2 = std::min(part2, v.part2);
+    }
+  }
+
+  std::cout << "Part 1: " << part1 << std::endl;
+  std::cout << "Part 2: " << part2 << std::endl;
+}

day23.cpp

@@ -1,3 +1,4 @@
+#include <array>
 #include <cstddef>
 #include <deque>
 #include <iostream>
@@ -15,16 +16,14 @@ namespace {
 struct Payload { ValueType x, y; };
 struct Packet { ValueType destination; Payload payload; };
 using Ethernet = std::deque<Packet>;
+using Machines = std::array<Machine, 50>;
 
-auto BuildNetwork(Machine m) -> std::vector<Machine> {
+auto BuildNetwork(Machine m) -> Machines {
-  std::vector<Machine> machines;
+  Machines machines;
-  machines.reserve(50);
-
   auto& i = std::get<Input>(Step(m)).input;
-  for (i = 0; i < 50; i++) {
+  for (i = 0; i < machines.size(); i++) {
-    machines.push_back(m);
+    machines[i] = m;
   }
-
   return machines;
 }
 
@@ -56,7 +55,7 @@ auto Interact(Ethernet & ethernet, Machine & m, std::optional<Payload> p) -> voi
 
 } // namespace
 
-auto main(int argc, char** argv) -> int {
+auto main(int const argc, char** const argv) -> int {
   auto fin = aocpp::Startup(argc, argv);
   auto machines = BuildNetwork(Machine{ParseStream(fin)});
   auto ethernet = Ethernet{};
@@ -67,7 +66,7 @@ auto main(int argc, char** argv) -> int {
 
   for(;;) {
     if (!ethernet.empty()) {
-      auto packet = ethernet.front();
+      auto const packet = ethernet.front();
       ethernet.pop_front();
       if (packet.destination == 255) {
         nat = packet.payload;

intcode/src/Interpreter.cpp

@@ -2,10 +2,10 @@
 
 namespace intcode {
 
-BadInstruction::BadInstruction(char const* what)
+BadInstruction::BadInstruction(char const* const what)
     : std::runtime_error{what} {}
 
-auto StepInput(Machine & m, ValueType input) -> void {
+auto StepInput(Machine & m, ValueType const input) -> void {
   std::get<Input>(Step(m)).input = input;
 }
 
@@ -15,67 +15,58 @@ auto StepOutput(Machine & m) -> ValueType {
 
 auto Step(Machine & m) -> std::variant<Input, Output, Halt> {
   for (;;) {
-    auto instruction = m.Next();
+    auto next = m.Next();
-    auto modes = instruction / 10;
+    auto const instruction = next % 100; next /= 100;
 
-    auto arg = [&]() -> ValueType & {
+    auto const arg = [&]() -> ValueType & {
       auto &v = m.Next();
-      switch ((modes /= 10) % 10) {
+      auto const mode = next % 10; next /= 10;
-      case 0:
+      switch (mode) {
-        return m.At(v);
+      case 0: return m.At(v);
-      case 1:
+      case 1: return v;
-        return v;
+      case 2: return m.Rel(v);
-      case 2:
+      default: throw BadInstruction{"invalid addressing mode"};
-        return m.Rel(v);
-      default:
-        throw BadInstruction{"invalid addressing mode"};
       }
     };
 
-    switch (instruction % 100) {
+    switch (instruction) {
-    case 1: {
+    case 1:
       arg() = arg() + arg();
       break;
-    }
 
-    case 2: {
+    case 2:
       arg() = arg() * arg();
       break;
-    }
 
-    case 3: {
+    case 3:
       return Input{arg()};
-    }
 
-    case 4: {
+    case 4:
       return Output{arg()};
-    }
 
     case 5: {
-      auto a = arg();
+      auto const a = arg();
-      auto b = arg();
+      auto const b = arg();
       if (a) { m.Goto(b); }
       break;
     }
 
     case 6: {
-      auto a = arg();
+      auto const a = arg();
-      auto b = arg();
+      auto const b = arg();
       if (!a) { m.Goto(b); }
       break;
     }
 
     case 7: {
-      auto a = arg();
+      auto const a = arg();
-      auto b = arg();
+      arg() = a < arg();
-      arg() = a < b; // order matters
       break;
     }
 
-    case 8: {
+    case 8:
       arg() = arg() == arg();
       break;
-    }
 
     case 9:
       m.Rebase(arg());
@@ -85,6 +76,7 @@ auto Step(Machine & m) -> std::variant<Input, Output, Halt> {
       return Halt{};
 
     default:
+    std::cout << instruction << std::endl;
       throw BadInstruction{"invalid opcode"};
     }
   }

intcode/src/Machine.cpp

@@ -5,17 +5,17 @@ namespace intcode {
 Machine::Machine() : rom_{}, ram_{}, pc_{0}, base_{0} {}
 
 Machine::Machine(std::vector<ValueType> program)
-    : rom_{program}, ram_{}, pc_{0}, base_{0} {}
+    : rom_{std::move(program)}, ram_{}, pc_{0}, base_{0} {}
 
-auto Machine::At(std::size_t i) -> ValueType & {
+auto Machine::At(std::size_t const i) -> ValueType & {
   return i < rom_.size() ? rom_[i] : ram_[i];
 }
 
-auto Machine::Rel(std::size_t i) -> ValueType & {
+auto Machine::Rel(std::size_t const i) -> ValueType & {
   return At(base_ + i);
 }
 
-auto Machine::Rebase(std::size_t offset) -> void {
+auto Machine::Rebase(std::size_t const offset) -> void {
   base_ += offset;
 }
 
@@ -23,7 +23,7 @@ auto Machine::Next() -> ValueType & {
   return At(pc_++);
 }
 
-auto Machine::Goto(std::size_t address) -> void {
+auto Machine::Goto(std::size_t const address) -> void {
   pc_ = address;
 }
 

lib/include/aocpp/Coord.hpp

@@ -40,6 +40,8 @@ auto CW(Coord) -> Coord;
 /// Rotate counter-clockwise
 auto CCW(Coord) -> Coord;
 
+auto Norm1(Coord) -> std::int64_t;
+
 /// Add two coordinates pairwise
 auto operator+(Coord, Coord) -> Coord;
 

lib/src/Coord.cpp

@@ -1,5 +1,7 @@
 #include <aocpp/Coord.hpp>
 
+#include <cstdlib>
+
 namespace aocpp {
 
 auto Draw(std::ostream & out, std::map<Coord, std::int64_t> image) -> void {
@@ -65,6 +67,10 @@ auto CCW(Coord c) -> Coord {
   return c;
 }
 
+auto Norm1(Coord c) -> std::int64_t {
+  return std::abs(c.x) + std::abs(c.y);
+}
+
 auto operator+(Coord a, Coord b) -> Coord {
   return {a.x + b.x, a.y + b.y};
 }