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