day_03.scala

import scala.io.Source

object Day03 {
  def main() = {
    val lines = Source.fromFile("day_03.input").getLines().toList

    val dupedItemsPerRucksackPriority =
      lines
        .map(duplicatedItemInRucksack)
        .map(itemPriority)
        .sum

    val dupedItemsAcrossTeamsPriority =
      lines
        .grouped(3)
        .map(duplicatedItemAcrossRucksacks)
        .map(itemPriority)
        .sum

    println(f"Part 1: ${dupedItemsPerRucksackPriority}")
    println(f"Part 2: ${dupedItemsAcrossTeamsPriority}")
  }

  def duplicatedItemInRucksack(line: String): Char = {
    val (firstHalf, secondHalf) = line.splitAt(line.length / 2)
    val firstCompartment = firstHalf.toSet
    val secondCompartment = secondHalf.toSet
    val commonItems: Set[Char] = firstCompartment & secondCompartment
    val List(item: Char) = commonItems.toList

    commonItems.toList match {
      case List(item: Char) => item
      case _ =>
        throw new IllegalArgumentException(
          f"Found multiple duplicated items in rucksack: ${line}, dupes: ${commonItems}"
        )
    }
  }

  def duplicatedItemAcrossRucksacks(lines: List[String]): Char = {
    val commonItems: Set[Char] = lines.map(_.toSet).reduce(_.intersect(_))
    val List(item: Char) = commonItems.toList
    item
  }

  def itemPriority(item: Char): Int = {
    if ('a' <= item && item <= 'z') {
      item.toInt - 'a' + 1
    } else if ('A' <= item && item <= 'Z') {
      item.toInt - 'A' + 27
    } else {
      throw new IllegalArgumentException(f"Unexpected character: ${item}")
    }
  }
}