2023, 09

jurisk · Dec 9, 2023 · 8dfdf6e · 8dfdf6e
1 parent cbcb948
commit 8dfdf6e
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Showing 2 changed files with 7 additions and 12 deletions.
diff --git a/scala2/src/main/scala/jurisk/adventofcode/y2023/Advent09.scala b/scala2/src/main/scala/jurisk/adventofcode/y2023/Advent09.scala
@@ -1,16 +1,15 @@
 package jurisk.adventofcode.y2023
 
-import jurisk.utils.CollectionOps.{EqIterableOps, IntegralIterableOps}
+import jurisk.utils.CollectionOps.{EqIterableOps, IntegralSeqOps}
 import jurisk.utils.FileInput._
 import jurisk.utils.Parsing.StringOps
 
 object Advent09 {
   type N     = Long
   type Input = List[List[N]]
 
-  private def extrapolatedValue(list: Iterable[N]): N =
-    if (list.allEqual(0)) 0
-    else list.last + extrapolatedValue(list.differencesUnsafe)
+  private def extrapolatedValue(list: Seq[N]): N =
+    if (list.allEqual(0)) 0 else list.last + extrapolatedValue(list.differences)
 
   def part1(input: Input): N = input.map(extrapolatedValue).sum
   def part2(input: Input): N = part1(input.map(_.reverse))

diff --git a/scala2/src/main/scala/jurisk/utils/CollectionOps.scala b/scala2/src/main/scala/jurisk/utils/CollectionOps.scala
@@ -31,14 +31,10 @@ object CollectionOps {
       seq.forall(_ === value)
   }
 
-  implicit class IntegralIterableOps[N: Integral](seq: Iterable[N]) {
-    def differencesUnsafe: Iterable[N] =
-      if (seq.isEmpty) {
-        sys.error("No differences possible for empty sequence")
-      } else {
-        (seq.init zip seq.tail) map { case (a, b) =>
-          b - a
-        }
+  implicit class IntegralSeqOps[N: Integral](seq: Seq[N]) {
+    def differences: Seq[N] =
+      seq.sliding2 map { case (a, b) =>
+        b - a
       }
   }