1 files changed, 16 insertions, 17 deletions

diff --git a/2025/src/day04.cpp b/2025/src/day04.cpp
index 295ed75..ef3b7f5 100644
--- a/2025/src/day04.cpp
+++ b/2025/src/day04.cpp
@@ -1,6 +1,9 @@
+#include <array>
 #include <filesystem>
 #include <fstream>
 #include <iostream>
+#include <map>
+#include <queue>
 #include <set>
 #include <string>
 #include <tuple>
@@ -30,7 +33,7 @@ read_file(const filesystem::path& filename)
         return grid;
 }
 
-set<Pos>
+array<Pos, 8>
 get_neighbours(const Pos& pos)
 {
         auto [col, row] = pos;
@@ -47,40 +50,35 @@ get_neighbours(const Pos& pos)
         };
 }
 
+size_t
+get_nneighbours(const set<Pos>& grid, const Pos& pos)
+{
+        return (size_t) ranges::count_if(get_neighbours(pos), [&](const auto& neighbour) { return grid.contains(neighbour); });
+}
+
 bool
 is_accessable(const set<Pos>& grid, const Pos& pos)
 {
-        long nneighbours = 0;
-        for ( const auto neighbour: get_neighbours(pos) ) {
-                if ( grid.contains(neighbour) ) {
-                        ++nneighbours;
-                }
-        }
-        return nneighbours < 4;
+        return get_nneighbours(grid, pos) < 4;
 }
 
 void
 part1(const set<Pos>& grid)
 {
-        long count = 0;
-        for ( const auto pos: grid ) {
-                if ( is_accessable(grid, pos) ) {
-                        ++count;
-                }
-        }
+        auto count = ranges::count_if(grid, [&](const auto& pos) { return is_accessable(grid, pos); });
         cout << "Part 1: " << count << '\n';
 }
 
 void
 part2(set<Pos> grid)
 {
-        auto old_size = grid.size();
+        const auto old_size = grid.size();
         while ( true ) {
-                set<Pos> remove;
+                vector<Pos> remove;
 
                 for ( const auto& pos: grid ) {
                         if ( is_accessable(grid, pos) ) {
-                                remove.insert(pos);
+                                remove.emplace_back(pos);
                         }
                 }
 
@@ -92,6 +90,7 @@ part2(set<Pos> grid)
                         grid.erase(pos);
                 }
         }
+
         cout << "Part 2: " << old_size - grid.size() << '\n';
 }