diff --git a/aoc/src/dev/ctsk/aoc/days/Day04.scala b/aoc/src/dev/ctsk/aoc/days/Day04.scala
index b2d2b5e..d154efc 100644
--- a/aoc/src/dev/ctsk/aoc/days/Day04.scala
+++ b/aoc/src/dev/ctsk/aoc/days/Day04.scala
@@ -1,49 +1,46 @@
 package dev.ctsk.aoc.days
 
 import dev.ctsk.aoc._
+import scala.compiletime.ops.double
+import scala.reflect.ClassTag
+import scala.collection.mutable.ArrayBuffer
 
 object Day04 extends Solver(4):
+  private val XMAS = "XMAS".r
+  private val REV_XMAS = "XMAS".reverse.r
+
+  def diagonals[A: ClassTag](m: Array[Array[A]]): Array[Array[A]] =
+    val diagonals = Array.fill(m.length + m(0).length - 1)(ArrayBuffer[A]())
+
+    for
+      i <- m.indices
+      j <- m(i).indices
+    do diagonals(i + j) :+= m(i)(j)
+
+    diagonals.map(_.toArray)
 
   def part1(lines: Array[Array[Char]]): Int =
-    def pad(front: Int, line: Array[Char], end: Int): Array[Char] =
-      Array.fill(front)('.') ++ line ++ Array.fill(end)('.')
-
     def count(line: Array[Char]) =
-      (0 until line.length - 3)
-        .count(idx => {
-          (line.slice(idx, idx + 4) sameElements Array('X', 'M', 'A', 'S'))
-          || (line.slice(idx, idx + 4) sameElements Array('S', 'A', 'M', 'X'))
-        })
+      val cs = ArrayCharSequence(line)
+      XMAS.findAllIn(cs).length + REV_XMAS.findAllIn(cs).length
 
-    lines.map(count(_)).sum
-      + lines.transpose.map(count(_)).sum
-      + lines.zipWithIndex
-        .map((line, index) => pad(index, line, lines.length - index))
-        .transpose
-        .map(count(_))
-        .sum
-      + lines.zipWithIndex
-        .map((line, index) => pad(lines.length - index, line, index))
-        .transpose
-        .map(count(_))
-        .sum
+    lines.map(count).sum
+      + lines.transpose.map(count).sum
+      + diagonals(lines).map(count).sum
+      + diagonals(lines.reverse).map(count).sum
 
   def part2(grid: Array[Array[Char]]): Int =
-    def countXMAS(g: Array[Array[Char]]): Int =
-      (for
-        i <- 0 until g.length - 2
-        j <- 0 until g(i).length - 2
-        if g(i)(j) == 'M' && g(i)(j + 2) == 'M'
-          && g(i + 1)(j + 1) == 'A'
-          && g(i + 2)(j) == 'S' && g(i + 2)(j + 2) == 'S'
-      yield 1).sum
+    var count = 0
 
-    List(
-      grid,
-      grid.reverse,
-      grid.transpose,
-      grid.transpose.reverse
-    ).map(countXMAS).sum
+    for
+      i <- 1 until grid.length - 1
+      j <- 1 until grid(i).length - 1
+      if grid(i)(j) == 'A'
+        & (grid(i - 1)(j - 1) + grid(i + 1)(j + 1) == 'S' + 'M')
+        & (grid(i - 1)(j + 1) + grid(i + 1)(j - 1) == 'S' + 'M')
+    do count += 1
+
+    count
 
   def run(input: String): (Timings, Solution) =
     var in = io.Source