Advent of Code 10.scala

import java.io.FileInputStream
import scala.io.StdIn

@main def solve10() =

  def solve1(numbers: Vector[Int]): Int = {
    val jolts = 0 +: numbers.sorted :+ (numbers.max + 3)
    val gabs = jolts.sliding(2).foldLeft(Map[Int, Int]()) { (acc, x) =>
      val gab = x(1) - x(0)
      acc.updated(gab, acc.getOrElse(gab, 0) + 1) 
    }
    gabs(1) * gabs(3)
  }

  def solve2(numbers: Vector[Int]): BigInt = {
    val jolts = 0 +: numbers.sorted :+ (numbers.max + 3)
    val numberOfWaysToArrange = jolts.indices.foldLeft(Array.fill(jolts.size)(BigInt(0))) { (acc, idx) =>
      if 0 == idx then
        acc(idx) = 1
      else
        (1 to 3).foreach(delta =>
          if 0 <= idx - delta && 3 >= jolts(idx) - jolts(idx - delta) then
            acc(idx) += acc(idx - delta)
        )
      acc
    }
    numberOfWaysToArrange.last
  }

  val in = new FileInputStream("example10-1.in")
  System.setIn(in)

  val inputs = Iterator.continually(StdIn.readLine()).takeWhile(_ != null).toVector
  val numbers = inputs.map { line => line.toInt }
  val answer1 = solve1(numbers)
  println(answer1)
  val answer2 = solve2(numbers)
  println(answer2)