Solve 2025 day 6 part 2

Author: sim642

src/main/scala/eu/sim642/adventofcode2025/Day6.scala

@@ -25,19 +25,52 @@ object Day6 {
     case "*" => Multiply
   }
 
-  def parseProblems(input: String): Seq[Problem] = {
-    input
-      .linesIterator
-      .map(_.trim.split(" +").toSeq)
-      .toSeq
-      .transpose
-      .map(s => Problem(s.init.map(_.toInt), parseProblemKind(s.last)))
+  trait Part {
+    def parseProblems(input: String): Seq[Problem]
+  }
+
+  object Part1 extends Part {
+    override def parseProblems(input: String): Seq[Problem] = {
+      input
+        .linesIterator
+        .map(_.trim.split(" +").toSeq)
+        .toSeq
+        .transpose
+        .map(s => Problem(s.init.map(_.toInt), parseProblemKind(s.last)))
+    }
+  }
+
+  object Part2 extends Part {
+    override def parseProblems(input: String): Seq[Problem] = {
+      val lines = input.linesIterator.toSeq
+      val maxLength = lines.map(_.length).max
+      val paddedLines = lines.map(_.padTo(maxLength, ' ')) // pad because test code has trimmed trailing whitespace
+      val cols = paddedLines.transpose
+
+      // TODO: split on Seq?
+      def helper(cols: Seq[Seq[Char]]): List[Problem] = {
+        val (problemCols, newCols) = cols.span(!_.forall(_ == ' '))
+        val problemKind = parseProblemKind(problemCols.head.last.toString)
+        val nums = problemCols.map(_.init.mkString("").trim.toInt)
+        val problem = Problem(nums, problemKind)
+        val rest = {
+          if (newCols.isEmpty)
+            Nil
+          else
+            helper(newCols.tail)
+        }
+        problem :: rest
+      }
+
+      helper(cols)
+    }
   }
 
   lazy val input: String = scala.io.Source.fromInputStream(getClass.getResourceAsStream("day6.txt")).mkString.trim
 
   def main(args: Array[String]): Unit = {
-    println(sumAnswers(parseProblems(input)))
+    println(sumAnswers(Part1.parseProblems(input)))
+    println(sumAnswers(Part2.parseProblems(input)))
 
     // part 1: 1615951811 - too low (Int overflowed in Problem#answer)
   }

src/test/scala/eu/sim642/adventofcode2025/Day6Test.scala

@@ -12,10 +12,18 @@ class Day6Test extends AnyFunSuite {
       |*   +   *   +""".stripMargin
 
   test("Part 1 examples") {
-    assert(sumAnswers(parseProblems(exampleInput)) == 4277556)
+    assert(sumAnswers(Part1.parseProblems(exampleInput)) == 4277556)
   }
 
   test("Part 1 input answer") {
-    assert(sumAnswers(parseProblems(input)) == 5361735137219L)
+    assert(sumAnswers(Part1.parseProblems(input)) == 5361735137219L)
+  }
+
+  test("Part 2 examples") {
+    assert(sumAnswers(Part2.parseProblems(exampleInput)) == 3263827)
+  }
+
+  test("Part 2 input answer") {
+    assert(sumAnswers(Part2.parseProblems(input)) == 11744693538946L)
   }
 }