Make Grid iterable

2017/22.cpp

@@ -17,13 +17,13 @@ auto Part1(aocpp::Grid const &input, std::int64_t reps = 10'000) -> std::int64_t
   std::unordered_set<aocpp::Coord> infected;
 
   // Initialize set of infected locations
-  input.each([&infected](auto const pos, auto const cell)
+  for (auto [pos, cell] : input)
   {
     if (cell == '#')
     {
       infected.insert(pos);
     }
-  });
+  }
 
   // Start in the middle
   aocpp::Coord pos;
@@ -62,13 +62,13 @@ auto Part2(aocpp::Grid const &input, std::int64_t reps = 10'000'000) -> std::int
   std::unordered_map<aocpp::Coord, char> cells;
 
   // Initialize set of infected locations
-  input.each([&cells](auto const pos, auto const cell)
+  for (auto [pos, cell] : input)
   {
     if (cell == '#')
     {
       cells.try_emplace(pos, '#');
     }
-  });
+  }
 
   // Start in the middle
   aocpp::Coord pos;

2018/15.cpp

@@ -60,11 +60,11 @@ Game::Game(Grid grid)
   , debug_out_{}
   {
     // set each unit to its initial hit points
-    grid_.each([&](auto k, auto v) {
+    for (auto [k, v] : grid_) {
       if (IsUnit(v)) {
         units_[k] = initial_hp;
       }
-    });
+    }
   }
 
 // Render the game as seen in the examples
@@ -166,9 +166,9 @@ auto Game::Simulate() -> std::optional<int> {
 
       // Detect when no targets remain for this unit and end the game
       auto game_over = true;
-      grid_.each([&](auto k, auto v) {
+      for (auto [k, v] : grid_) {
         if (IsOpposed(active_team, v)) game_over = false;
-      });
+      }
       if (game_over) {
         int total_hp = 0;
         for (auto const& [_,v] : units_) { total_hp += v; }

2019/10.cpp

@@ -70,23 +70,23 @@ auto ClearView(Grid const& grid, Coord src, Coord dst) -> bool {
 auto Part1(Grid const& grid) {
   std::size_t best = 0;
   Coord base {};
-  grid.each([&](Coord src, char s) {
+  for (auto [src, s] : grid) {
     if ('#' == s) {
       std::size_t visible = 0;
-      grid.each([&](Coord dst, char d){
+      for (auto [dst, d] : grid) {
         if ('#' == d && src != dst) {
           if (ClearView(grid, src, dst)) {
             visible++;
           }
         }
-      });
+      }
       
       if (visible > best) {
         best = visible;
         base = src;
       }
     }
-  });
+  }
   return std::make_pair(best, base);
 }
 
@@ -94,11 +94,11 @@ auto Part2(Grid const& grid, Coord base, std::size_t n) {
   std::map<Rational<std::int64_t>, std::vector<Coord>> targets;
 
   // arrange all the other asteroids by their angle relative to the base
-  grid.each([&](Coord c, char v){
+  for (auto [c, v] : grid){
     if (c != base && v == '#') {
       targets[angle(c-base)].push_back(c);
     }
-  });
+  }
 
   // Sort to vectors per angle such that the nearest asteroids are at
   // the end of the list

2019/17.cpp

@@ -66,14 +66,14 @@ auto ComputePath(Grid const& grid)
 {
   // Determine starting location and direction
   Coord start{}, step{};
-  grid.each([&](Coord c, char v) {
+  for (auto [c, v] : grid) {
     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] == '#';

2019/18.cpp

@@ -41,11 +41,11 @@ auto SetKey(Doors& doors, char key) {
 
 auto FindFeatures(Grid const& grid) -> Features {
   Features features;
-  grid.each([&](Coord c, char v) {
+  for (auto [c, v] : grid) {
     if ('#' != v && '.' != v) {
       features[v] = c;
     }
-  });
+  }
   return features;
 }
 

2019/24.cpp

@@ -27,9 +27,9 @@ auto FindBugs(Grid const& grid) -> std::vector<Coord> {
   std::int64_t w = grid.Cols();
   std::int64_t h = grid.Rows();
 
-  grid.each([&](Coord c, char v) {
+  for (auto [c, v] : grid) {
     if (v == '#') result.push_back(c);
-  });
+  }
   return result;
 }
 

2022/08.cpp

@@ -22,7 +22,7 @@ Dir directions[4] {Up, Down, Left, Right};
 auto Part1(Grid const& grid) -> std::int64_t
 {
   std::int64_t result {0};
-  grid.each([&](Coord const c, char const v) {
+  for (auto [c, v] : grid) {
     result += std::any_of(
       std::begin(directions), std::end(directions),
       [&](Dir const dir) {
@@ -31,14 +31,14 @@ auto Part1(Grid const& grid) -> std::int64_t
         }
         return true;
       });
-  });
+  }
   return result;
 }
 
 auto Part2(Grid const& grid) -> std::int64_t
 {
   std::int64_t result {0};
-  grid.each([&](Coord const c, char const v) {
+  for (auto [c, v] : grid) {
     auto score = std::transform_reduce(
       std::begin(directions), std::end(directions),
       std::int64_t{1}, std::multiplies(), // product
@@ -51,7 +51,7 @@ auto Part2(Grid const& grid) -> std::int64_t
         return count;
       });
     if (result < score) result = score;
-  });
+  }
   return result;
 }
 

2022/12.cpp

@@ -27,13 +27,13 @@ auto Parse(std::istream & in) -> std::tuple<Coord, std::vector<Coord>, Coord, Gr
   auto& end = std::get<2>(result);
   auto& grid = std::get<3>(result);
 
-  grid.each([&](Coord c, char v) {
+  for (auto [c, v] : grid) {
     switch (v) {
       case 'S': grid[c] = 'a'; start1 = c; break;
       case 'E': grid[c] = 'z'; end   = c; break;
       case 'a': starts2.push_back(c);     break;
     }
-  });
+  }
 
   return result;
 }

lib/CMakeLists.txt

@@ -1,3 +1,3 @@
-add_library(aocpp src/Startup.cpp src/Coord.cpp src/Parsing.cpp)
+add_library(aocpp src/Startup.cpp src/Coord.cpp src/Parsing.cpp src/Grid.cpp)
 target_include_directories(aocpp PUBLIC include)
 target_link_libraries(aocpp Boost::headers)

lib/include/aocpp/Grid.hpp

@@ -1,7 +1,6 @@
 #ifndef AOCPP_GRID_HPP_
 #define AOCPP_GRID_HPP_
 
-#include <concepts>
 #include <iostream>
 #include <stdexcept>
 #include <type_traits>
@@ -12,6 +11,31 @@
 
 namespace aocpp {
 
+struct Grid;
+
+struct GridElement {
+  const Coord pos;
+  char elt;
+};
+
+class GridIterator {
+  Grid const& grid_;
+  std::int64_t x_, y_;
+
+  public:
+  GridIterator(Grid const& grid, std::int64_t x, std::int64_t y)
+  : grid_{grid}, x_{x}, y_{y} {}
+
+  auto operator++() -> GridIterator&;
+
+  auto operator*() -> GridElement;
+
+  auto operator==(GridIterator const& rhs) const -> bool
+  {
+    return x_ == rhs.x_ && y_ == rhs.y_;
+  }
+};
+
 struct Grid {
   std::vector<std::string> rows;
   std::size_t columns;
@@ -57,28 +81,16 @@ struct Grid {
         }
         result.rows.emplace_back(std::move(line));
       }
-    } else {
-      result.columns = 0;
     }
     return result;
   }
 
-  /**
-   * @brief Apply the callback function across all elements of the grid.
-   * 
-   * @tparam F Type of callback
-   * @param f Callback function
-   */
-  template <std::invocable<Coord, char> F>
-  auto each(F f = F{}) const -> void {
-    auto const h = rows.size();
-    for (std::size_t y = 0; y < h; y++) {
-      auto const& row = rows[y];
-      auto const w = row.size();
-      for (std::size_t x = 0; x < w; x++) {
-        f(Coord{static_cast<std::int64_t>(x), static_cast<std::int64_t>(y)}, row[x]);
-      }
-    }
+  auto begin() const -> GridIterator {
+    return GridIterator{*this, 0, 0};
+  }
+
+  auto end() const -> GridIterator {
+    return GridIterator{*this, 0, static_cast<std::int64_t>(rows.size())};
   }
 };
 

lib/src/Grid.cpp

@@ -0,0 +1,19 @@
+#include "aocpp/Grid.hpp"
+
+namespace aocpp {
+auto GridIterator::operator*() -> GridElement
+{
+    return {{x_, y_}, grid_[Coord{x_, y_}]};
+}
+
+auto GridIterator::operator++() -> GridIterator &
+{
+    if (++x_ == grid_.columns)
+    {
+        x_ = 0;
+        y_++;
+    }
+
+    return *this;
+}
+} // namespace