AoC day 14

import java.security.MessageDigest

import scala.annotation.tailrec
import scala.collection.mutable

object day14 {

  def salt: String = "cuanljph"
  def match3 = "(.)\\1{2,}".r
  def match5 = "(.)\\1{4,}".r
  def digest = MessageDigest.getInstance("MD5")

  def md5(s: String, repeat: Int): String = {
    def hash(h: String) =
      digest.digest(h.getBytes).map("%02x".format(_)).mkString
    (1 to repeat).par.foldLeft(s)((a, _) => hash(a))
  }

  def findKeys(repeat: Int): List[Int] = {

    val triplets = mutable.Map[Char, List[Int]]().withDefaultValue(Nil)

    @tailrec
    def inner(id: Int, acc: List[Int]): List[Int] = acc match {
      case x if x.length >= 64 => acc
      case x =>
        val hash = md5(salt + id, repeat)
        val quintuplet = match5.findFirstIn(hash)
        if (quintuplet.isDefined) {
          val matches = triplets(quintuplet.get.head).filter(_ + 1000 > id)
          triplets(quintuplet.get.head) = List(id)
          inner(id + 1, x ::: matches)
        }
        else {
          val triplet = match3.findFirstIn(hash)
          if (triplet.isDefined) {
            triplets(triplet.get.head) = triplets(triplet.get.head) :+ id
          }
          inner(id + 1, x)
        }
    }
    inner(0, Nil).sorted
  }

  def run = {
    println((findKeys(1) take 64).last)
    println((findKeys(2017) take 64).last)
  }

}