day 12 puzzle 2

src/day12/puzzle2.typ

@@ -0,0 +1,151 @@
+#import "/src/utils.typ": *
+
+#let offsets = (
+  (-1, 0),
+  (0, -1),
+  (1, 0),
+  (0, 1)
+)
+
+#let in-grid(w, h, x, y) = {
+  return 0 <= x and x < w and 0 <= y and y < h
+}
+
+#let solve(input) = {
+  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)
+
+  let zone-grid = ((none,) * w,) * h
+  let zone-id = 0
+  let zone-sides = ()
+  let zone-areas = ()
+
+  for y in range(h) {
+    for x in range(w) {
+      if zone-grid.at(y).at(x) != none {
+        continue
+      }
+      let char = grid.at(y).at(x)
+      let area = 0
+      let borders = 0
+      let next-cells = ((x, y),)
+
+      while next-cells.len() != 0 {
+        let (cx, cy) = next-cells.remove(0)
+        zone-grid.at(cy).at(cx) = zone-id
+        area += 1
+        for (dx, dy) in offsets {
+          let (x2, y2) = (cx + dx, cy + dy)
+          if (x2, y2) in next-cells {
+            continue
+          }
+          if in-grid(x2, y2) {
+            if zone-grid.at(y2).at(x2) == zone-id {
+              continue
+            }
+            let char2 = grid.at(y2).at(x2)
+            if char2 == char {
+              next-cells.push((x2, y2))
+            }
+          }
+        }
+      }
+      zone-areas.push(area)
+      zone-sides.push(0)
+      zone-id += 1
+    }
+  }
+
+  let first-zone0 = -1
+  let last-zone0 = -1
+  for y in range(h) {
+    let first-zone = zone-grid.at(y).at(0)
+    let last-zone = zone-grid.at(y).at(w - 1)
+    if first-zone0 != first-zone {
+      zone-sides.at(first-zone) += 1
+    }
+    if last-zone0 != last-zone {
+      zone-sides.at(last-zone) += 1
+    }
+    first-zone0 = first-zone
+    last-zone0 = last-zone
+  }
+
+  first-zone0 = -1
+  last-zone0 = -1
+  for x in range(w) {
+    let first-zone = zone-grid.at(0).at(x)
+    let last-zone = zone-grid.at(h - 1).at(x)
+    if first-zone0 != first-zone {
+      zone-sides.at(first-zone) += 1
+    }
+    if last-zone0 != last-zone {
+      zone-sides.at(last-zone) += 1
+    }
+    first-zone0 = first-zone
+    last-zone0 = last-zone
+  }
+
+  for x in range(w - 1) {
+    let zone-a0 = -1
+    let zone-b0 = -1
+    for y in range(h) {
+      let zone-a = zone-grid.at(y).at(x)
+      let zone-b = zone-grid.at(y).at(x + 1)
+      if zone-a != zone-b {
+        if zone-a != zone-a0 {
+          zone-sides.at(zone-a) += 1
+        }
+        if zone-b != zone-b0 {
+          zone-sides.at(zone-b) += 1
+        }
+        zone-a0 = zone-a
+        zone-b0 = zone-b
+      } else {
+        zone-a0 = -1
+        zone-b0 = -1
+      }
+    }
+  }
+
+  for y in range(h - 1) {
+    let zone-a0 = -1
+    let zone-b0 = -1
+    for x in range(w) {
+      let zone-a = zone-grid.at(y).at(x)
+      let zone-b = zone-grid.at(y + 1).at(x)
+      if zone-a != zone-b {
+        if zone-a != zone-a0 {
+          zone-sides.at(zone-a) += 1
+        }
+        if zone-b != zone-b0 {
+          zone-sides.at(zone-b) += 1
+        }
+        zone-a0 = zone-a
+        zone-b0 = zone-b
+      } else {
+        zone-a0 = -1
+        zone-b0 = -1
+      }
+    }
+  }
+
+  let total = range(zone-id).map(i => {
+    zone-sides.at(i) * zone-areas.at(i)
+  })
+  return total.sum()
+}
+
+#show-puzzle(
+  12, 2,
+  solve,
+  example: (
+    "1": 80,
+    "2": 436,
+    "3": 1206,
+    "4": 236,
+    "5": 368
+  )
+)