diff --git a/input/day09 b/input/day09
new file mode 100644
index 0000000..c8563ea
--- /dev/null
+++ b/input/day09
@@ -0,0 +1,8 @@
+7,1
+11,1
+11,7
+9,7
+9,5
+2,5
+2,3
+7,3
diff --git a/src/day09.scala b/src/day09.scala
new file mode 100644
index 0000000..e0b2d09
--- /dev/null
+++ b/src/day09.scala
@@ -0,0 +1,64 @@
+package aoc
+package day09
+
+import scala.math.{min, max}
+
+val dayNumber = "09"
+
+@main def part1: Unit =
+  println(part1(loadInput(dayNumber)))
+
+@main def part2: Unit =
+  println(part2(loadInput(dayNumber)))
+
+def part1(input: String): Long =
+  val tiles = input.split('\n').map { case s"$x,$y" => (x = x.toLong, y = y.toLong) }
+  tiles
+    .combinations(2)
+    .collect {
+      case Array(a, b) if a != b =>
+        ((a.x - b.x + 1) * (a.y - b.y + 1)).abs
+    }.max
+
+def part2(input: String): Long =
+  val points  = input.split('\n').map { case s"$x,$y" => (x = x.toLong, y = y.toLong) }
+  val polygon = points
+
+  def corners(ax: Long, ay: Long, bx: Long, by: Long) =
+    List((ax, ay), (ax, by), (ay, bx), (bx, by))
+
+  def isInside(x: Long, y: Long) =
+    val counter = polygon.sliding(2).foldLeft(0) { case (counter, Array(a, b)) =>
+      if y > min(a.y, b.y) && y <= max(a.y, b.y) && x <= max(a.x, b.x) then
+        val xinters = (y - a.y) * (b.x - a.x) / (b.y - a.y) + a.x
+        counter + (if a.x == b.x || x <= xinters then 1 else 0)
+      else counter
+    }
+    counter % 2 == 1
+
+  println(isInside(7, 1))
+
+  println(isInside(7, 2))
+  println(isInside(0, 0))
+  points
+    .combinations(2)
+    .collect {
+      case Array(a, b) if a != b && corners(a.x, a.y, b.x, b.y).forall((x, y) => isInside(x, y)) =>
+        println(corners(a.x, a.y, b.x, b.y))
+        (a, b)
+    }
+    .map((a, b) => ((a.x - b.x + 1) * (a.y - b.y + 1)).abs)
+    .max
+
+  // if (p.y > MIN(p1.y,p2.y)) {
+  //   if (p.y <= MAX(p1.y,p2.y)) {
+  //     if (p.x <= MAX(p1.x,p2.x)) {
+  //       if (p1.y != p2.y) {
+  //         xinters = (p.y-p1.y)*(p2.x-p1.x)/(p2.y-p1.y)+p1.x;
+  //         if (p1.x == p2.x || p.x <= xinters)
+  //           counter++;
+  //       }
+  //     }
+  //   }
+  // }
+end part2