aoc2018.day1.scala

package com.matthicks.aoc2018

import scala.annotation.tailrec
import scala.io.Source

object Day1 {
  private lazy val data: List[Int] = {
    Source.fromURL(getClass.getClassLoader.getResource("day1.txt")).getLines().toList.map(_.toInt)
  }

  def main(args: Array[String]): Unit = println(s"Part 1: ${part1(data)}, Part 2: ${part2(data)}")

  def part1(changes: List[Int]): Int = changes.sum
  def part2(changes: List[Int]): Int = recurse(Iterator.continually(changes).flatten)

  @tailrec
  private def recurse(iterator: Iterator[Int],
                      current: Int = 0,
                      states: Set[Int] = Set.empty): Int = current + iterator.next() match {
    case state if states.contains(state) => state
    case state => recurse(iterator, state, states + state)
  }
}