day 20 puzzle 1

progress.yaml

@@ -35,4 +35,6 @@
 18:
   stars: 2
 19:
-  stars: 2
+  stars: 2
+20:
+  stars: 1

res/examples/day20.txt

@@ -0,0 +1,15 @@
+###############
+#...#...#.....#
+#.#.#.#.#.###.#
+#S#...#.#.#...#
+#######.#.#.###
+#######.#.#...#
+#######.#.###.#
+###..E#...#...#
+###.#######.###
+#...###...#...#
+#.#####.#.###.#
+#.#...#.#.#...#
+#.#.#.#.#.#.###
+#...#...#...###
+###############

src/day20/puzzle1.typ

@@ -0,0 +1,128 @@
+#import "/src/utils.typ": *
+
+#let offsets = (
+  (1, 0),
+  (0, 1),
+  (-1, 0),
+  (0, -1)
+)
+
+#let EMPTY = "."
+#let WALL = "#"
+#let START = "S"
+#let END = "E"
+
+#let in-grid(w, h, x, y) = {
+  return 0 <= x and x < w and 0 <= y and y < h
+}
+
+#let count-shortcuts(grid, w, h, save, path) = {
+  let in-grid = in-grid.with(w, h)
+  let total = 0
+  for (x1, y1) in path {
+    let v1 = grid.at(y1).at(x1)
+
+    for (dx1, dy1) in offsets {
+      let (x2, y2) = (x1 + dx1, y1 + dy1)
+      if not in-grid(x2, y2) {
+        continue
+      }
+      let v2 = grid.at(y2).at(x2)
+      if v2 < 0 {
+        for (dx2, dy2) in offsets {
+          let (x3, y3) = (x2 + dx2, y2 + dy2)
+          if not in-grid(x3, y3) {
+            continue
+          }
+          let v3 = grid.at(y3).at(x3)
+          if v3 > 0 {
+            if v3 - v1 >= save + 2 {
+              total += 1
+            }
+          }
+        }
+      }
+    }
+  }
+  return total
+}
+
+#let solve(input, save: 1) = {
+  let input-grid = input.split("\n").map(l => l.clusters())
+
+  let w = input-grid.first().len()
+  let h = input-grid.len()
+  let in-grid = in-grid.with(w, h)
+
+  let grid = ((-1,)*w,)*h
+  let start = none
+  let end = none
+  for y in range(h) {
+    for x in range(w) {
+      let c = input-grid.at(y).at(x)
+      if c == WALL {
+        continue
+      }
+      if c == START {
+        start = (x, y)
+      } else if c == END {
+        end = (x, y)
+      }
+      grid.at(y).at(x) = 0
+    }
+  }
+
+  let (x, y) = start
+  let (ex, ey) = end
+  let path = ()
+
+  while x != ex or y != ey {
+    path.push((x, y))
+    grid.at(y).at(x) = path.len()
+    for (dx, dy) in offsets {
+      let (x2, y2) = (x + dx, y + dy)
+      if not in-grid(x2, y2) {
+        continue
+      }
+      let v = grid.at(y2).at(x2)
+      if v == 0 {
+        (x, y) = (x2, y2)
+        break
+      }
+    }
+  }
+  path.push((x, y))
+  grid.at(y).at(x) = path.len()
+
+  return count-shortcuts(
+    grid, w, h,
+    save,
+    path
+  )
+}
+
+#let examples = (
+  (64, 1),
+  (40, 1),
+  (38, 1),
+  (36, 1),
+  (20, 1),
+  (12, 3),
+  (10, 2),
+  (8, 4),
+  (6, 2),
+  (4, 14),
+  (2, 14),
+)
+#let n-tot = 0
+#let examples2 = ()
+#for (save, cnt) in examples {
+  n-tot += cnt
+  examples2.push((result: n-tot, args: (save: save)))
+}
+
+#show-puzzle(
+  20, 1,
+  solve.with(save: 100),
+  example: examples2
+)