Day 15 part 2

README.md

@@ -115,4 +115,4 @@ Part 2: By changing the order the rounded rocks to also do a one pass processing
 
 Part 1: Suprisingly simple !
 
-Part 2: The main difficulty is understanding the instructions.
+Part 2: The main difficulty is understanding the instructions and then find out how to model the data.

src/main/scala/day15.scala

@@ -3,19 +3,38 @@ import zio.Console._
 
 object Day15 extends ZIOAppDefault {
 
-  def hashCmd(cmd:String) : Int = 
-    cmd.foldLeft(0)( (a,c) => {
-        val na = (a + c)*17 % 256
-        na
+  def hashCmd(cmd: String): Int =
+    cmd.foldLeft(0)((a, c) => {
+      val na = (a + c) * 17 % 256
+      na
     })
 
-  def part1(cmds: List[String]) = 
+  def part1(cmds: List[String]) =
     cmds.flatMap(_.split(',')).map(hashCmd).sum
 
+  def part2(cmds: List[String]) =
+    val m = cmds.flatMap(_.split(',')).foldLeft(Map[Int, List[(String, Int)]]()) { (m, cmd) =>
+      (m, cmd.split('=').toList, cmd.split('-').toList) match
+        case (m, label :: fl :: _, _) =>
+          m.updatedWith(hashCmd(label)) {
+            case Some(l) if l.exists(_._1 == label) => Some(l.map(p => if p._1 == label then (label, fl.toInt) else p))
+            case Some(l)                            => Some(l.appended((label, fl.toInt)))
+            case None                               => Some(List((label, fl.toInt)))
+          }
+        case (m, _, label :: _) =>
+          m.updatedWith(hashCmd(label)) {
+            case Some(l) => Some(l.filter(_._1 != label))
+            case l       => l
+          }
+    }
+    m.toList.flatMap { case (boxIndex, l) =>
+      (l zip (1 to l.length)).map(e => ((boxIndex + 1) * e._2 * e._1._2))
+    }.sum
 
   def run =
     for {
       v <- Day1.readFile("day15_input.txt")
       _ <- printLine(s"part1=${part1(v)}")
+      _ <- printLine(s"part2=${part2(v)}")
     } yield ()
 }

src/test/scala/day15_test.scala

@@ -9,4 +9,8 @@ class Day15Test {
   def testPart1() =
     assertEquals(1320, Day15.part1(cmds))
 
+  @Test
+  def testPart2() =
+    assertEquals(145, Day15.part2(cmds))
+
 }