day 8 puzzle 1

progress.yaml

@@ -12,3 +12,5 @@
   stars: 2
 7:
   stars: 2
+8:
+  stars: 1

res/examples/day8.txt

@@ -0,0 +1,12 @@
+............
+........0...
+.....0......
+.......0....
+....0.......
+......A.....
+............
+............
+........A...
+.........A..
+............
+............

src/day8/puzzle1.typ

@@ -0,0 +1,51 @@
+#import "/src/utils.typ": *
+
+#let in-grid(w, h, x, y) = {
+  return 0 <= x and x < w and 0 <= y and y < h
+}
+
+#let solve(input) = {
+  let by-freq = (:)
+  let antinodes = ()
+
+  let grid = input.split("\n").map(l => l.clusters())
+  let w = grid.first().len()
+  let h = grid.len()
+
+  let in-grid = in-grid.with(w, h)
+
+  for y in range(h) {
+    for x in range(w) {
+      let c = grid.at(y).at(x)
+      if c == "." {
+        continue
+      }
+      if c not in by-freq {
+        by-freq.insert(c, ())
+      }
+
+      for (x2, y2) in by-freq.at(c) {
+        let (dx, dy) = (x2 - x, y2 - y)
+        let node1 = (x - dx, y - dy)
+        let node2 = (x2 + dx, y2 + dy)
+
+        if in-grid(..node1) and node1 not in antinodes {
+          antinodes.push(node1)
+        }
+
+        if in-grid(..node2) and node2 not in antinodes {
+          antinodes.push(node2)
+        }
+      }
+      by-freq.at(c).push((x, y))
+    }
+  }
+
+  return antinodes.len()
+}
+
+#show-puzzle(
+  8, 1,
+  solve,
+  example: 14
+)