Day 6

Day5.scala

@@ -102,6 +102,7 @@ def toLocation(seed: Long) =
   loop("seed", seed)
 
 def toLocation(seed: LRange) =
+  @scala.annotation.tailrec
   def loop(entryName: String, value: Seq[LRange]): Seq[LRange] =
     if entryName == "location" then value
     else

Day6.scala

@@ -0,0 +1,48 @@
+package aoc.day6
+
+import aoc._
+
+case class Race(time: Long, distance: Long):
+  def waysToWin =
+    val minTime = search(0, (time - 1) / 2)
+    val midOk = if time % 2 == 0 && withHold(time / 2) > distance then 1L else 0
+    2 * (minTime to (time - 1) / 2).length + midOk
+  @scala.annotation.tailrec
+  private final def search(min: Long, max: Long): Long =
+    if min >= max then min
+    else
+      val mid = (max + min) / 2
+      if withHold(mid) <= distance then search(mid + 1, max)
+      else search(min, mid)
+  def withHold(k: Long) = k * (time - k)
+
+object Parser extends CommonParser:
+  val nums = rep1(num)
+  def time[T](nums: Parser[T]) = "Time:" ~> nums
+  def distance[T](nums: Parser[T]) = "Distance:" ~> nums
+
+  val bigNum = rep1("""\d+""".r) ^^ (_.mkString.toLong)
+
+  def races(ss: Seq[String]) = ss match {
+    case Seq(t, d) =>
+      parse(time(nums), t).get.zip(parse(distance(nums), d).get).map(Race(_, _))
+  }
+
+  def bigRace(ss: Seq[String]) = ss match {
+    case Seq(t, d) =>
+      Race(parse(time(bigNum), t).get, parse(distance(bigNum), d).get)
+  }
+
+def part1 =
+  val races = Parser.races(lines.toSeq)
+  val res = races.map(_.waysToWin).product
+  println(res)
+
+def part2 =
+  val race = Parser.bigRace(lines.toSeq)
+  val res = race.waysToWin
+  println(res)
+
+@main def Day6(part: Int) = part match
+  case 1 => part1
+  case 2 => part2

inputs/day6.input

@@ -0,0 +1,2 @@
+Time:        56     97     77     93
+Distance:   499   2210   1097   1440