Day 10: Use transform_reduce instead of for-loop

Author: zeichensystem

CMakeLists.txt

@@ -37,7 +37,7 @@ list(LENGTH TARGETS NUM_TARGETS)
 foreach(current_target IN LISTS TARGETS)
  add_executable(${current_target} ${current_target}/${current_target}.cpp)
  set_target_properties(${current_target} PROPERTIES DEBUG_POSTFIX ${CMAKE_DEBUG_POSTFIX})
- target_include_directories(${current_target} PRIVATE "${CMAKE_CURRENT_SOURCE_DIR}/aoclib/") 
+ target_include_directories(${current_target} PRIVATE "${CMAKE_CURRENT_SOURCE_DIR}/") 
 
  target_compile_options(${current_target} PRIVATE ${WARNING_FLAGS_CXX} $<$<CONFIG:Debug>:${DBG_FLAGS_CXX}>)
  target_link_options(${current_target} PRIVATE ${WARNING_FLAGS_CXX} $<$<CONFIG:Debug>:${DBG_FLAGS_CXX}>)

aoclib/grid.hpp

@@ -341,6 +341,8 @@ class Grid
  }
 
 public: 
+ typedef ElemType value_type;
+
  Grid() = default; 
 
  Grid(const std::vector<RowType>& rows) 

aoclib/vec.hpp

@@ -9,6 +9,7 @@ namespace aocutil
 template<typename T>
 struct Vec2 
 {
+ typedef T value_type;
  T x, y; 
 
  Vec2 operator+(const Vec2& v) const 

day-10/day-10.cpp

@@ -1,7 +1,8 @@
 #include <stack>
-#include "../aoclib/aocio.hpp"
-#include "../aoclib/grid.hpp"
-#include "../aoclib/vec.hpp"
+#include <numeric>
+#include "aoclib/aocio.hpp"
+#include "aoclib/grid.hpp"
+#include "aoclib/vec.hpp"
 
 /*
  Problem: https://adventofcode.com/2024/day/10
@@ -23,13 +24,14 @@ using Vec2 = aocutil::Vec2<int>;
 int part_one(const std::vector<std::string>& lines, bool part_two = false)
 {
  Grid<int> height_map; 
- for (const auto& line : lines) {
- std::vector<int> row; 
+
+ for (const auto& line : lines) {
+ std::vector<decltype(height_map)::value_type> row; 
  std::transform(line.cbegin(), line.cend(), std::back_inserter(row), [](char c) {
  return aocio::parse_digit(c).value();
  });
  height_map.push_row(row);
-  }
+ }
 
  const auto get_adjacent = [&height_map = std::as_const(height_map)](const Vec2& pos) {
  const auto dirs = aocutil::all_dirs_vec2<int>(); 
@@ -42,21 +44,19 @@ int part_one(const std::vector<std::string>& lines, bool part_two = false)
  return neighbors; 
  };
 
- int result = 0; 
- const std::vector<Vec2> trailheads = height_map.find_elem_positions_if([](int h) {return h == 0;}); 
- for (const auto& trailhead : trailheads) {
- int score = 0; 
+ const auto trailhead_score = [&height_map = std::as_const(height_map), &get_adjacent, part_two](const Vec2& trailhead) -> int {
+ int score = 0;
  std::stack<Vec2> positions; 
  positions.push(trailhead);
  Grid<bool> reached(height_map.width(), height_map.height(), false);
 
  while (!positions.empty()) { // Depth-first search.
  const Vec2 pos = positions.top(); 
  positions.pop();
- const int current_height = height_map.get(pos);
+ const auto current_height = height_map.get(pos);
  std::vector<Vec2> adjacent = get_adjacent(pos); 
  for (const auto& adj_pos : adjacent) {
- int neighbor_height = height_map.get(adj_pos); 
+ const auto neighbor_height = height_map.get(adj_pos); 
  if (neighbor_height == current_height + 1) {
  if (neighbor_height == 9 && !reached.get(adj_pos)) {
  reached.set(adj_pos, !part_two); // Only use the "reached" grid for Part 1 (i.e. count all paths for Part 2)
@@ -67,9 +67,11 @@ int part_one(const std::vector<std::string>& lines, bool part_two = false)
  }
  }
  }
- result += score; 
- }
- return result;
+ return score;
+ }; 
+
+ const std::vector<Vec2> trailheads = height_map.find_elem_positions_if([](auto h) {return h == 0;}); 
+ return std::transform_reduce(trailheads.cbegin(), trailheads.cend(), int{0}, std::plus{}, trailhead_score);
 }
 
 int part_two(const std::vector<std::string>& lines)