diff --git a/README.md b/README.md
index 5a9ef5b..307ccb3 100644
--- a/README.md
+++ b/README.md
@@ -5,11 +5,11 @@ This repo contains my attempt at this year's Advent of Code (2023)
 I will try and do some problems (probably not all of them) in Scala
 
 ## Progress:
-#### Stars: 16 / 50
+#### Stars: 17 / 50
 |        Mon        |        Tue        |        Wed        |        Thu        |        Fri        |        Sat        |        Sun        |
 |:-----------------:|:-----------------:|:-----------------:|:-----------------:|:-----------------:|:-----------------:|:-----------------:|
 |                   |                   |                   |                   | 1<br>:star::star: | 2<br>:star::star: | 3<br>:star::star: |
-| 4<br>:star::star: | 5<br>:star::star: | 6<br>:star::star: | 7<br>:star::star: | 8<br>:star::star: |         9         |        10         |
+| 4<br>:star::star: | 5<br>:star::star: | 6<br>:star::star: | 7<br>:star::star: | 8<br>:star::star: |    9<br>:star:    |        10         |
 |        11         |        12         |        13         |        14         |        15         |        16         |        17         |
 |        18         |        19         |        20         |        21         |        22         |        23         |        24         |
 |        25         |                   |                   |                   |                   |                   |                   |
\ No newline at end of file
diff --git a/src/day9/Puzzle1.scala b/src/day9/Puzzle1.scala
new file mode 100644
index 0000000..81d1f27
--- /dev/null
+++ b/src/day9/Puzzle1.scala
@@ -0,0 +1,41 @@
+package day9
+
+import scala.collection.mutable
+import scala.io.{BufferedSource, Source}
+import scala.util.matching.Regex
+import scala.util.matching.Regex.Match
+
+object Puzzle1 {
+  var series: Array[Series] = Array.empty
+
+  def loadInput(path: String): Unit = {
+    val source: BufferedSource = Source.fromFile(path)
+    val lines: Array[String] = source.getLines().toArray
+
+    series = new Array(lines.length)
+
+    for ((line: String, i: Int) <- lines.zipWithIndex) {
+      series(i) = new Series(line.split(" ").map(_.toInt))
+    }
+
+    source.close()
+  }
+
+  def solve(path: String): Int = {
+    loadInput(path)
+
+    var solution: Int = 0
+
+    for (s: Series <- series) {
+      s.computeDiffs()
+      solution += s.extrapolate()
+    }
+
+    return solution
+  }
+
+  def main(args: Array[String]): Unit = {
+    val solution: Int = solve("./res/day9/input1.txt")
+    println(solution)
+  }
+}
diff --git a/src/day9/Series.scala b/src/day9/Series.scala
new file mode 100644
index 0000000..df546dc
--- /dev/null
+++ b/src/day9/Series.scala
@@ -0,0 +1,30 @@
+package day9
+
+import scala.collection.mutable.ArrayBuffer
+
+class Series {
+  private val values: ArrayBuffer[Array[Int]] = new ArrayBuffer()
+  def this(initialValues: Array[Int]) = {
+    this()
+    values.addOne(initialValues.concat(Array(0)))
+  }
+
+  def computeDiffs(): Unit = {
+    while (!(values.last.dropRight(1).distinct.length == 1 && values.last(0) == 0)) {
+      val diffs: Array[Int] = new Array(values.last.length-1)
+      for (i: Int <- 0 until diffs.length-1) {
+        diffs(i) = values.last(i+1) - values.last(i)
+      }
+      values.addOne(diffs)
+    }
+  }
+
+  def extrapolate(): Int = {
+    val len: Int = values(0).length
+    values.last(values.last.length-1) = 0
+    for (i: Int <- values.length-2 to 0 by -1) {
+      values(i)(len-i-1) = values(i)(len-i-2) + values(i+1)(len-i-2)
+    }
+    return values(0).last
+  }
+}
diff --git a/tests/day9/Puzzle1Test.scala b/tests/day9/Puzzle1Test.scala
new file mode 100644
index 0000000..1d8e14f
--- /dev/null
+++ b/tests/day9/Puzzle1Test.scala
@@ -0,0 +1,9 @@
+package day9
+
+import org.scalatest.funsuite.AnyFunSuite
+
+class Puzzle1Test extends AnyFunSuite {
+  test("Puzzle1.solve") {
+    assert(Puzzle1.solve("tests_res/day9/input1.txt") == 114)
+  }
+}
diff --git a/tests_res/day9/input1.txt b/tests_res/day9/input1.txt
new file mode 100644
index 0000000..70c5595
--- /dev/null
+++ b/tests_res/day9/input1.txt
@@ -0,0 +1,3 @@
+0 3 6 9 12 15
+1 3 6 10 15 21
+10 13 16 21 30 45
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