day 4 puzzle 2

progress.yaml

@@ -4,3 +4,5 @@
   stars: 2
 3:
   stars: 2
+4:
+  stars: 2

res/examples/day4.txt

@@ -0,0 +1,10 @@
+MMMSXXMASM
+MSAMXMSMSA
+AMXSXMAAMM
+MSAMASMSMX
+XMASAMXAMM
+XXAMMXXAMA
+SMSMSASXSS
+SAXAMASAAA
+MAMMMXMMMM
+MXMXAXMASX

src/day4/puzzle1.typ

@@ -0,0 +1,57 @@
+#import "/src/utils.typ": *
+
+#let check-xmas(lines, ox, oy) = {
+  let w = lines.first().len()
+  let h = lines.len()
+
+  let total = 0
+  for dy in (-1, 0, 1) {
+    for dx in (-1, 0, 1) {
+      if dx == 0 and dy == 0 {
+        continue
+      }
+      let buffer = ""
+      let x = ox
+      let y = oy
+      for i in range(4) {
+        buffer += lines.at(y).at(x)
+        x += dx
+        y += dy
+        if (
+          not "XMAS".starts-with(buffer) or
+          x < 0 or x >= w or
+          y < 0 or y >= h
+        ) {
+          break
+        }
+      }
+      if buffer == "XMAS" {
+        total += 1
+      }
+    }
+  }
+  return total
+}
+
+#let solve(input) = {
+  let lines = input.split("\n")
+  let w = lines.first().len()
+  let h = lines.len()
+
+  let total = 0
+  for y in range(h) {
+    for x in range(w) {
+      if lines.at(y).at(x) == "X" {
+        total += check-xmas(lines, x, y)
+      }
+    }
+  }
+
+  return total
+}
+
+#show-puzzle(
+  4, 1,
+  solve,
+  example: 18
+)

src/day4/puzzle2.typ

@@ -0,0 +1,33 @@
+#import "/src/utils.typ": *
+
+#let solve(input) = {
+  let lines = input.split("\n")
+  let w = lines.first().len()
+  let h = lines.len()
+
+  let perms = (("M", "S"), ("S", "M"))
+  let total = 0
+  for y in range(1, h - 1) {
+    for x in range(1, w - 1) {
+      if lines.at(y).at(x) == "A" {
+        let tl = lines.at(y - 1).at(x - 1)
+        let tr = lines.at(y - 1).at(x + 1)
+        let bl = lines.at(y + 1).at(x - 1)
+        let br = lines.at(y + 1).at(x + 1)
+        let tlbr = (tl, br)
+        let bltr = (bl, tr)
+        if tlbr in perms and bltr in perms {
+          total += 1
+        }
+      }
+    }
+  }
+
+  return total
+}
+
+#show-puzzle(
+  4, 2,
+  solve,
+  example: 9
+)