Solve 2024 day 1 part 2

Author: sim642

src/main/scala/eu/sim642/adventofcode2024/Day1.scala

@@ -1,5 +1,7 @@
 package eu.sim642.adventofcode2024
 
+import eu.sim642.adventofcodelib.IterableImplicits._
+
 object Day1 {
 
   def totalListDistance(lists: Seq[(Int, Int)]): Int = {
@@ -9,6 +11,14 @@ object Day1 {
       .sum
   }
 
+  def similarityScore(lists: Seq[(Int, Int)]): Int = {
+    val (list1, list2) = lists.unzip
+    val list2Count = list2.groupCount(identity).withDefaultValue(0)
+    list1
+      .map(i => i * list2Count(i))
+      .sum
+  }
+
   def parsePair(s: String): (Int, Int) = s match {
     case s"$i   $j" => (i.toInt, j.toInt)
   }
@@ -19,5 +29,6 @@ object Day1 {
 
   def main(args: Array[String]): Unit = {
     println(totalListDistance(parseLists(input)))
+    println(similarityScore(parseLists(input)))
   }
 }

src/test/scala/eu/sim642/adventofcode2024/Day1Test.scala

@@ -20,4 +20,12 @@ class Day1Test extends AnyFunSuite {
   test("Part 1 input answer") {
     assert(totalListDistance(parseLists(input)) == 1666427)
   }
+
+  test("Part 2 examples") {
+    assert(similarityScore(parseLists(exampleInput)) == 31)
+  }
+
+  test("Part 2 input answer") {
+    assert(similarityScore(parseLists(input)) == 24316233)
+  }
 }