diff --git a/2019/24.cpp b/2019/24.cpp
index aac02d9..9b9abb9 100644
--- a/2019/24.cpp
+++ b/2019/24.cpp
@@ -1,19 +1,14 @@
 #include <algorithm>
+#include <concepts>
 #include <cstdint>
 #include <iostream>
-#include <iomanip>
-#include <fstream>
 #include <iterator>
-#include <stdexcept>
-#include <vector>
+#include <map>
 #include <set>
+#include <stdexcept>
 #include <string>
 #include <tuple>
-#include <bitset>
-#include <deque>
-#include <cctype>
-#include <queue>
-#include <map>
+#include <vector>
 
 #include <aocpp/Startup.hpp>
 #include <aocpp/Coord.hpp>
@@ -39,7 +34,7 @@ struct Map {
 };
 
 auto FindBugs(Map const& map) {
-  std::set<Coord> result;
+  std::vector<Coord> result;
 
   std::int64_t w = map.rows[0].size();
   std::int64_t h = map.rows.size();
@@ -47,92 +42,72 @@ auto FindBugs(Map const& map) {
   for (std::int64_t x = 0; x < w; x++) {
     for (std::int64_t y = 0; y < h; y++) {
       Coord const c = {x,y};
-      if (map[c] == '#') result.insert(c);
+      if (map[c] == '#') result.push_back(c);
     }
   }
   return result;
 }
 
-auto Neighbor1(Coord c) {
-  std::vector<Coord> result;
-  result.reserve(4);
-  if (c.x > 0) result.push_back(Left(c));
-  if (c.x < 4) result.push_back(Right(c));
-  if (c.y > 0) result.push_back(Up(c));
-  if (c.y < 4) result.push_back(Down(c));
-  return result;
-}
-
-auto Neighbor2(std::pair<Coord, std::int64_t> cd) {
-  auto [c,d] = cd;
-  std::vector<std::pair<Coord, std::int64_t>> result;
-  result.reserve(8);
-
-  if (c.x == 3 && c.y == 2) {
-    for (std::int64_t yi = 0; yi < 5; yi++) {
-      result.push_back({{4,yi},d+1});
-    }
-  } else if (c.x > 0) {
-    result.push_back({Left(c),d});
-  } else {
-    result.push_back({{1,2},d-1});
+struct Neighbor1 {
+  auto operator()(Coord c, auto f) const -> void {
+    if (c.x > 0) f(Left(c));
+    if (c.x < 4) f(Right(c));
+    if (c.y > 0) f(Up(c));
+    if (c.y < 4) f(Down(c));
   }
+};
 
-  if (c.x == 1 && c.y == 2) {
-    for (std::int64_t yi = 0; yi < 5; yi++) {
-      result.push_back({{0,yi},d+1});
-    }
-  } else if (c.x < 4) {
-    result.push_back({Right(c),d});
-  } else {
-    result.push_back({{3,2},d-1});
+struct Neighbor2 {
+  using C3 = std::pair<Coord, std::int64_t>;
+  auto operator()(C3 cd, auto f) const -> void {
+    auto const [c,d] = cd;
+
+    auto left_neighbors = [&f](Coord c, std::int64_t d, auto k_, auto k) {
+      c = k_(c);
+      if (c.x == 1 && c.y == 0) {
+        for (std::int64_t yi = -2; yi <= 2; yi++) {
+          f({k({2,yi}),d+1});
+        }
+      } else if (c.x > -2) {
+        f({k(Left(c)),d});
+      } else {
+        f({k({-1,0}),d-1});
+      }
+    };
+    auto id = [](Coord i) { return i; };
+    left_neighbors(c, d, id, id);
+    left_neighbors(c, d, Turn180, Turn180);
+    left_neighbors(c, d, CW, CCW);
+    left_neighbors(c, d, CCW, CW);
   }
+};
 
-  if (c.x == 2 && c.y == 3) {
-    for (std::int64_t xi = 0; xi < 5; xi++) {
-      result.push_back({{xi,4},d+1});
-    }
-  } else if (c.y > 0) {
-    result.push_back({Up(c),d});
-  } else {
-    result.push_back({{2,1},d-1});
-  }
-
-  if (c.x == 2 && c.y == 1) {
-    for (std::int64_t xi = 0; xi < 5; xi++) {
-      result.push_back({{xi,0},d+1});
-    }
-  } else if (c.y < 4) {
-    result.push_back({Down(c),d});
-  } else {
-    result.push_back({{2,3},d-1});
-  }
-
-  return result;
-}
-
-template<class F, class C>
-auto Step(std::set<C> const& bugs, F neighbors)
+template<typename F, typename C>
+auto Step(std::vector<C> const& bugs, F with_neighbors = F{})
 {
   std::map<C, int> adjacent;
   for (auto const& x : bugs) {
-    for (auto const& n : neighbors(x)) {
-      adjacent[n]++;
-    }
+    with_neighbors(x, [&adjacent](C n) -> void { adjacent[n]++; });
   }
 
-  std::set<C> result;
+  std::vector<C> result;
   for (auto const& [k,v] : adjacent) {
     switch (v) {
-      case 1: result.insert(k); break;
-      case 2: if (!bugs.contains(k)) result.insert(k); break;
+    case 1:
+      result.push_back(k);
+      break;
+    case 2:
+      if (!std::binary_search(bugs.begin(), bugs.end(), k)) {
+        result.push_back(k);
+        break;
+      }
     }
   }
 
   return result;
 }
 
-auto Bio(std::set<Coord> const& bugs) -> std::uint32_t {
+auto Bio(std::vector<Coord> const& bugs) -> std::uint32_t {
   std::uint32_t result = 0;
   for (auto const& c : bugs) {
     result |= 1U << (5 * c.y + c.x);
@@ -140,23 +115,23 @@ auto Bio(std::set<Coord> const& bugs) -> std::uint32_t {
   return result;
 }
 
-auto Part1(std::set<Coord> const& bugs) -> std::uint32_t {
+auto Part1(std::vector<Coord> const& bugs) -> std::uint32_t {
   auto cursor = bugs;
   std::set<std::uint32_t> seen;
   std::uint32_t bio;
   while (seen.insert(bio = Bio(cursor)).second) {
-    cursor = Step(cursor, Neighbor1);
+    cursor = Step<Neighbor1>(cursor);
   }
   return bio;
 }
 
-auto Part2(std::set<Coord> const& bugs) {
-  std::set<std::pair<Coord,std::int64_t>> bugs2;
-  for (auto const& x : bugs) {
-    bugs2.insert({x,0});
+auto Part2(std::vector<Coord> const& bugs) {
+  std::vector<std::pair<Coord,std::int64_t>> bugs2;
+  for (auto const& [x,y] : bugs) {
+    bugs2.push_back({{x-2,y-2},0});
   }
   for (int i = 0; i < 200; i++) {
-    bugs2 = Step(bugs2, Neighbor2);
+    bugs2 = Step<Neighbor2>(bugs2);
   }
   return bugs2.size();
 }
diff --git a/lib/include/aocpp/Coord.hpp b/lib/include/aocpp/Coord.hpp
index e9c8ab5..81ddef8 100644
--- a/lib/include/aocpp/Coord.hpp
+++ b/lib/include/aocpp/Coord.hpp
@@ -40,6 +40,8 @@ auto CW(Coord) -> Coord;
 /// Rotate counter-clockwise
 auto CCW(Coord) -> Coord;
 
+auto Turn180(Coord) -> Coord;
+
 auto Norm1(Coord) -> std::int64_t;
 
 /// Add two coordinates pairwise
diff --git a/lib/src/Coord.cpp b/lib/src/Coord.cpp
index e749f08..7800f5b 100644
--- a/lib/src/Coord.cpp
+++ b/lib/src/Coord.cpp
@@ -62,9 +62,11 @@ auto CW(Coord c) -> Coord {
 }
 
 auto CCW(Coord c) -> Coord {
-  c = Invert(c);
-  c.y = -c.y;
-  return c;
+  return CW(CW(CW(c)));
+}
+
+auto Turn180(Coord c) -> Coord {
+  return CW(CW(c));
 }
 
 auto Norm1(Coord c) -> std::int64_t {