17

2019/17.cpp

@@ -0,0 +1,226 @@
+#include <algorithm>
+#include <iostream>
+#include <map>
+#include <tuple>
+#include <utility>
+#include <vector>
+
+#include <aocpp/Coord.hpp>
+#include <aocpp/Grid.hpp>
+#include <aocpp/Startup.hpp>
+#include <intcode/intcode.hpp>
+
+using namespace aocpp;
+using namespace intcode;
+
+namespace {
+
+auto GatherOutput(Machine m) -> Grid
+{
+    Grid grid;
+    bool eol = true; // next output starts a new line
+
+    Run(m, []() -> ValueType {
+      throw std::runtime_error{"input not supported"};
+    },
+    [&](ValueType c) -> void {
+      if (eol) {
+        grid.rows.emplace_back();
+        eol = false;
+      }
+      if ('\n' == c) {
+        eol = true;
+      } else {
+        grid.rows.back().push_back(static_cast<char>(c));}
+      }
+    );
+    return grid;
+}
+
+/// Find all the 4-way intersections.
+/// @return Sum of product of coordinates
+auto ScaffoldAlignments(Grid const& grid) -> std::size_t
+{
+  std::int64_t answer = 0;
+  std::int64_t h = grid.rows.size();
+  for (std::int64_t y = 1; y+1 < h; y++) {
+    auto const& row = grid.rows[y];
+    std::int64_t w = row.size();
+    for (std::int64_t x = 1; x+1 < w; x++) {
+      Coord c = {x,y};
+      if (grid[c] == '#' &&
+        grid[Up(c)] == '#' &&
+        grid[Down(c)] == '#' &&
+        grid[Left(c)] == '#' &&
+        grid[Right(c)] == '#')
+      {
+        answer += x*y;
+      }
+    }
+  }
+  return answer;
+}
+
+auto ComputePath(Grid const& grid)
+  -> std::vector<std::pair<char, std::int64_t>>
+{
+  // Determine starting location and direction
+  Coord start{}, step{};
+  grid.each([&](Coord c, char v) {
+    switch (v) {
+      case '^': start = c; step = { 0, -1}; break;
+      case '>': start = c; step = { 0,  1}; break;
+      case '<': start = c; step = {-1,  0}; break;
+      case 'v': start = c; step = { 0,  1}; break;
+    }
+  });
+
+  auto is_path = [&](Coord c) {
+    return grid.contains(c) && grid[c] == '#';
+  };
+
+  std::vector<std::pair<char, std::int64_t>> result;
+  for(;;) {
+    char dir;
+    if (is_path(start + CW(step))) {
+      dir = 'R';
+      step = CW(step);
+    } else if (is_path(start + CCW(step))) {
+      dir = 'L';
+      step = CCW(step);
+    } else {
+      return result;
+    }
+
+    std::int64_t n = 0;
+    while (is_path(start + step)) {
+      start += step;
+      n++;
+    }
+    result.emplace_back(dir, n);
+  }
+}
+
+template <typename It>
+auto RenderCommands(It begin, It end) -> std::string
+{
+  std::string result;
+  while (begin != end) {
+    auto const& [m,n] = *begin++;
+    result += m;
+    result += ',';
+    result += std::to_string(n);
+    result += ',';
+  }
+  result.pop_back(); // trailing comma
+  return result;
+}
+
+template<class InputIter1, class InputIter2>
+auto constexpr prefix(
+  InputIter1 first1, InputIter1 last1,
+  InputIter2 first2, InputIter2 last2
+) -> bool
+{
+  for(;;) {
+    if (first1 == last1) return true;
+    if (first2 == last2) return false;
+    if (*first1++ != *first2++) return false;
+  }
+}
+
+using Path = std::vector<std::pair<char, std::int64_t>>;
+
+auto ComputeProgramLoop(
+  Path::const_iterator begin,
+  Path::const_iterator end,
+  std::vector<char> & solution,
+  std::map<char, std::pair<Path::const_iterator, Path::const_iterator>> & subroutines
+) -> bool
+{
+  // no path left to encode, we're done
+  if (begin == end) return true;
+
+  // Try using an existing subroutine
+  for (auto const& [k,v] : subroutines) {
+    if (prefix(v.first, v.second, begin, end)) {
+      solution.push_back(k);
+      auto begin_ = begin + (v.second - v.first);
+      if (ComputeProgramLoop(begin_, end, solution, subroutines)) return true;
+      solution.pop_back(); // rollback k
+    }
+  }
+
+  // Try allocating a new subroutine
+  if (subroutines.size() == 3) return false;
+  auto next_routine = 'A' + subroutines.size();
+  auto sub = subroutines.insert({next_routine, {}}).first;
+  solution.push_back(next_routine);
+
+  // Divide begin-end into begin-cursor and cursor-end
+  // Assign begin-end to a new subroutine and recursively solve
+  for (
+    auto cursor = begin+1;
+    cursor != end && RenderCommands(begin, cursor).size() <= 20;
+    ++cursor
+  ) {
+    sub->second = {begin, cursor};
+    if (ComputeProgramLoop(cursor, end, solution, subroutines)) return true;
+  }
+
+  // Deallocate the new subroutine; there was no solution
+  subroutines.erase(sub);
+  solution.pop_back();
+  return false;
+}
+
+auto ComputeProgram(Path const& path) -> std::string {
+  std::vector<char> solution;
+  std::map<char, std::pair<Path::const_iterator, Path::const_iterator>> subroutines;
+  
+  if (!ComputeProgramLoop(path.begin(), path.end(), solution, subroutines)) {
+    throw std::runtime_error{"no solution found"};
+  }
+
+  std::string result;
+  for (char c : solution) {
+    result += c;
+    result += ',';
+  }
+  result.back() = '\n';
+
+  for (auto const& [_,v] : subroutines) {
+    result += RenderCommands(v.first, v.second);
+    result += '\n';
+  }
+  result += "n\n"; // no video feed
+
+  return result;
+}
+
+auto GatherScore(Machine m, std::string const& program) -> ValueType {
+  ValueType score {};
+  auto it = program.begin();
+  m.At(0) = 2; // put into fancy mode
+  Run(m,
+    [&]() -> ValueType {
+      if (it < program.end()) { return *it++; }
+      throw std::runtime_error{"insufficient input"};
+    },
+    [&](ValueType o) { score = o; });
+  return score;
+}
+
+} // namespace
+
+auto main(int argc, char** argv) -> int {
+  auto machine = Machine{ParseStream(aocpp::Startup(argc, argv))};
+  auto grid = GatherOutput(machine);
+  auto part1 = ScaffoldAlignments(grid);
+  auto path = ComputePath(grid);
+  auto program = ComputeProgram(path);
+  std::cout << "Part 1: " << part1 << std::endl;
+  
+  auto part2 = GatherScore(std::move(machine), program);
+  std::cout << "Part 2: " << part2 << std::endl;
+}

2019/CMakeLists.txt

@@ -43,6 +43,9 @@ target_link_libraries(14 aocpp)
 add_executable(15 15.cpp)
 target_link_libraries(15 aocpp intcode)
 
+add_executable(17 17.cpp)
+target_link_libraries(17 aocpp intcode)
+
 add_executable(18 18.cpp)
 target_link_libraries(18 aocpp)
 

lib/include/aocpp/Grid.hpp

@@ -13,6 +13,14 @@ namespace aocpp {
 struct Grid {
   std::vector<std::string> rows;
 
+  auto contains(Coord c) const -> bool {
+    return 
+         0 <= c.x
+      && 0 <= c.y
+      && c.y < rows.size()
+      && c.x < rows[c.y].size();
+  }
+
   auto operator[](Coord c)       -> char& { return rows[c.y][c.x]; }
   auto operator[](Coord c) const -> char  { return rows[c.y][c.x]; }