Deduplicate in 2023 day 9

sim642 · Dec 9, 2023 · 264576f · 264576f
1 parent f9f5540
commit 264576f
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Showing 2 changed files with 31 additions and 31 deletions.
diff --git a/src/main/scala/eu/sim642/adventofcode2023/Day9.scala b/src/main/scala/eu/sim642/adventofcode2023/Day9.scala
@@ -4,30 +4,26 @@ object Day9 {
 
   type History = Seq[Int]
 
-  def nextValue(history: History): Int = {
-    val differences = LazyList.iterate(history)(history =>
-      (history lazyZip history.tail).map(-_ + _)
-    )
-    val nonZeroDifferences = differences.takeWhile(!_.forall(_ == 0))
-    nonZeroDifferences
-      .map(_.last)
-      .sum
+  def difference(history: History): History = (history.tail lazyZip history).map(_ - _)
+
+  trait Part {
+    def extrapolate(history: History): Int
+
+    def sumExtrapolated(histories: Seq[History]): Int = histories.map(extrapolate).sum
   }
 
-  def sumNextValues(histories: Seq[History]): Int = histories.map(nextValue).sum
-
-  def prevValue(history: History): Int = {
-    // TODO: deduplicate
-    val differences = LazyList.iterate(history)(history =>
-      (history lazyZip history.tail).map(-_ + _)
-    )
-    val nonZeroDifferences = differences.takeWhile(!_.forall(_ == 0))
-    nonZeroDifferences
-      .map(_.head)
-      .foldRight(0)((a, b) => a - b)
+  object Part1 extends Part {
+    override def extrapolate(history: History): Int = {
+      LazyList.iterate(history)(difference)
+        .takeWhile(!_.forall(_ == 0))
+        .map(_.last)
+        .sum
+    }
   }
 
-  def sumPrevValues(histories: Seq[History]): Int = histories.map(prevValue).sum
+  object Part2 extends Part {
+    override def extrapolate(history: History): Int = Part1.extrapolate(history.reverse)
+  }
 
 
   def parseHistories(input: String): Seq[History] =
@@ -36,7 +32,7 @@ object Day9 {
   lazy val input: String = io.Source.fromInputStream(getClass.getResourceAsStream("day9.txt")).mkString.trim
 
   def main(args: Array[String]): Unit = {
-    println(sumNextValues(parseHistories(input)))
-    println(sumPrevValues(parseHistories(input)))
+    println(Part1.sumExtrapolated(parseHistories(input)))
+    println(Part2.sumExtrapolated(parseHistories(input)))
   }
 }
diff --git a/src/test/scala/eu/sim642/adventofcode2023/Day9Test.scala b/src/test/scala/eu/sim642/adventofcode2023/Day9Test.scala
@@ -11,28 +11,32 @@ class Day9Test extends AnyFunSuite {
       |10 13 16 21 30 45""".stripMargin
 
   test("Part 1 examples") {
+    import Part1._
+
     val histories = parseHistories(exampleInput)
 
-    assert(nextValue(histories(0)) == 18)
-    assert(nextValue(histories(1)) == 28)
-    assert(nextValue(histories(2)) == 68)
+    assert(extrapolate(histories(0)) == 18)
+    assert(extrapolate(histories(1)) == 28)
+    assert(extrapolate(histories(2)) == 68)
 
-    assert(sumNextValues(histories) == 114)
+    assert(sumExtrapolated(histories) == 114)
   }
 
   test("Part 1 input answer") {
-    assert(sumNextValues(parseHistories(input)) == 1708206096)
+    assert(Part1.sumExtrapolated(parseHistories(input)) == 1708206096)
   }
 
   test("Part 2 examples") {
+    import Part2._
+
     val histories = parseHistories(exampleInput)
 
-    assert(prevValue(histories(0)) == -3)
-    assert(prevValue(histories(1)) == 0)
-    assert(prevValue(histories(2)) == 5)
+    assert(extrapolate(histories(0)) == -3)
+    assert(extrapolate(histories(1)) == 0)
+    assert(extrapolate(histories(2)) == 5)
   }
 
   test("Part 2 input answer") {
-    assert(sumPrevValues(parseHistories(input)) == 1050)
+    assert(Part2.sumExtrapolated(parseHistories(input)) == 1050)
   }
 }