1 files changed, 33 insertions, 0 deletions
diff --git a/src/2021/day5/aoc.h b/src/2021/day5/aoc.h
index c57f439..bd8c346 100644
--- a/src/2021/day5/aoc.h
+++ b/src/2021/day5/aoc.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include "common.h"
+#include <math.h>
 
 namespace aoc2021 {
 
@@ -8,9 +9,41 @@ struct line {
   struct point {
     int x;
     int y;
+
+    bool operator<(const point& p) const noexcept { return x < p.x ? true : x > p.x ? false : y < p.y; }
+    point move_h(int d) { return {x + d, y}; }
+    point move_v(int d) { return {x, y + d}; }
+    point move_p(int d) { return {x + d, y + d}; }
+    point move_d(int d) { return {x + d, y - d}; }
   };
   point p1;
   point p2;
+
+  bool is_vertical() const noexcept { return p1.x == p2.x; }
+  bool is_horizontal() const noexcept { return p1.y == p2.y; }
+  bool is_diagonal() const noexcept { return std::abs(p2.x - p1.x) == std::abs(p2.y - p1.y); }
+
+  template <typename F>
+  void traverse(F&& f) const noexcept {
+    auto next = [this](point x) {
+      if (is_vertical()) {
+        return x.move_v(1);
+      }
+      if (is_horizontal()) {
+        return x.move_h(1);
+      }
+      if (is_diagonal()) {
+        return p2.y > p1.y ? x.move_p(1) : x.move_d(1);
+      }
+      return x;
+    };
+    point p = p1;
+    while (p < p2) {
+      f(p);
+      p = next(p);
+    }
+    f(p); // p == p2
+  }
 };
 
 std::pair<int, int> day5(line_view);