Day 4 part 2

src/main/scala/day4.scala

@@ -2,8 +2,11 @@ import zio._
 import zio.Console._
 
 object Day4 extends ZIOAppDefault {
-  def cardValue(card: String) =
-    val winningNumbers :: draw :: _ = card.split(':')(1).split('|').toList
+  def parseCard(card: String): (Int, Int) =
+    val idString :: numbers :: _ = card.split(':').toList
+    val id = idString.split(' ').last.toInt
+    val winningNumbers :: draw :: _ = numbers.split('|').toList
+
     def toSet(numbers: String) = numbers
       .split(' ')
       .flatMap {
@@ -12,14 +15,23 @@ object Day4 extends ZIOAppDefault {
       }
       .toSet
     val nbWinningNumbers = (toSet(winningNumbers) intersect toSet(draw)).size
-    math.pow(2, nbWinningNumbers - 1).toInt
+    (id, nbWinningNumbers)
 
   def part1(cards: List[String]) =
-    cards.map(cardValue).sum
+    cards.map { card => math.pow(2, parseCard(card)._2 - 1).toInt }.sum
+
+  def part2(cards: List[String]) =
+    val cm = cards.map(parseCard).toMap
+
+    def countCards(index: Int): Int =
+      1 + ((index + 1) to (index + cm(index))).map(countCards).sum
+
+    (1 to cm.size).map(countCards).sum
 
   def run =
     for {
       v <- Day1.readFile("day4_input.txt")
       _ <- printLine(s"part1=${part1(v)}")
+      _ <- printLine(s"part2=${part2(v)}")
     } yield ()
 }

src/test/scala/day4_test.scala

@@ -12,11 +12,19 @@ class Day4Test {
     "Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11"
   )
 
+  val winningNumbers = Set(41, 48, 83, 86, 17)
+  val draw = Set(83, 86, 6, 31, 17, 9, 48, 53)
+
   @Test
-  def testCardValue() =
-    assertEquals(8, Day4.cardValue(cards(0)))
+  def testParseCard() =
+    assertEquals((1, 4), Day4.parseCard(cards(0)))
 
   @Test
   def testPart1() =
     assertEquals(13, Day4.part1(cards))
+
+  @Test
+  def testPart2() =
+    assertEquals(30, Day4.part2(cards))
+
 }