started day 16 puzzle 1

src/day16/puzzle1.typ

@@ -0,0 +1,67 @@
+#import "/src/utils.typ": *
+
+#let START = "S"
+#let END = "E"
+#let WALL = "#"
+#let EMPTY = "."
+
+#let offsets = (
+  (1, 0),
+  (0, 1),
+  (-1, 0),
+  (0, -1)
+)
+
+#let solve(input) = {
+  let grid = input.split("\n").map(l => l.clusters())
+  let w = grid.first().len()
+  let h = grid.len()
+
+  let (sx, sy) = (0, 0)
+  let (ex, ey) = (0, 0)
+  for y in range(h) {
+    for x in range(w) {
+      let c = grid.at(y).at(x)
+      if c == START {
+        (sx, sy) = (x, y)
+      } else if c == END {
+        (ex, ey) = (x, y)
+      }
+    }
+  }
+
+  let choices = ((sx, sy, 0, 0),)
+  let (x, y, dir, score) = (0, 0, 0, 0)
+  while choices.len() != 0 {
+    let min-score = calc.min(..choices.map(c => c.last()))
+    let i = choices.position(c => c.last() == min-score)
+    (x, y, dir, score) = choices.remove(i)
+    for (d, (dx, dy)) in offsets.enumerate() {
+      // Ignore backflips
+      if calc.abs(d - dir) == 2 {
+        continue
+      }
+      let (x2, y2) = (x + dx, y + dy)
+      let c = grid.at(y2).at(x2)
+      if c == WALL {
+        continue
+      }
+      let score2 = score + 1 + if d != dir {1000} else {0}
+      if c == END {
+        return score2
+      }
+      choices.push((x2, y2, d, score2))
+    }
+    break
+  }
+  return 0
+}
+
+#show-puzzle(
+  16, 1,
+  solve,
+  example: (
+    "1": 7036,
+    "2": 11048
+  )
+)