diff --git a/src/day09.scala b/src/day09.scala
index 2154a4b..e1cbc10 100644
--- a/src/day09.scala
+++ b/src/day09.scala
@@ -11,25 +11,20 @@ val dayNumber = "09"
 @main def part2: Unit =
   println(part2(loadInput(dayNumber)))
 
-@tailrec def generateDifferences(acc: Array[Array[Long]]): Array[Array[Long]] =
-  if acc.last.forall(_ == 0) then acc
-  else
-    generateDifferences(
-      acc.appended(
-        acc.last.sliding(2).map { case Array(l, r) => r - l }.toArray
+def findNextValue(history: Array[Long]): Long =
+  @tailrec def aux(history: Array[Long], acc: Long): Long =
+    if history.forall(_ == 0) then acc
+    else
+      aux(
+        history.sliding(2).map { case Array(l, r) => r - l }.toArray,
+        acc + history.last
       )
-    )
+  aux(history, 0)
 
 def part1(input: String): String =
   val readings = input.split('\n').map(_.split(' ').map(_.toLong))
-  def findNextValue(history: Array[Long]): Long =
-    generateDifferences(Array(history)).map(_.last).sum
   readings.map(findNextValue).sum.toString
 
 def part2(input: String): String =
   val readings = input.split('\n').map(_.split(' ').map(_.toLong))
-  def findPreviousValue(history: Array[Long]): Long =
-    generateDifferences(Array(history))
-      .map(_.head)
-      .reduceRight((v, acc) => v - acc)
-  readings.map(findPreviousValue).sum.toString
+  readings.map(_.reverse).map(findNextValue).sum.toString