Advent of Code 2021-10.scala

import java.io.FileInputStream
import scala.annotation.tailrec
import scala.io.StdIn


def parse(text: String): Either[Char, Vector[Char]] =
  @tailrec
  def _parse(acc: Vector[Char], index: Int): Either[Char, Vector[Char]] =
    if text.length <= index then
      Right(acc)
    else
      text(index) match
        case c @ ('(' | '[' | '{' | '<') =>
          _parse(acc :+ c, index + 1)
        case ')' if acc.lastOption.contains('(') =>
          _parse(acc.init, index + 1)
        case ')' =>
          Left(')')
        case ']' if acc.lastOption.contains('[') =>
          _parse(acc.init, index + 1)
        case ']' =>
          Left(']')
        case '}' if acc.lastOption.contains('{') =>
          _parse(acc.init, index + 1)
        case '}' =>
          Left('}')
        case '>' if acc.lastOption.contains('<') =>
          _parse(acc.init, index + 1)
        case '>' =>
          Left('>')
  _parse(Vector(), 0)



def solve10_1(inputs: Vector[String]): Int =
  inputs.foldLeft(0) { (acc, v) =>
    val score = parse(v) match
      case Left(')') => 3
      case Left(']') => 57
      case Left('}') => 1197
      case Left('>') => 25137
      case _ => 0
    score + acc
  }

def scoreOfAutocomplete(text: Vector[Char]): BigInt =
  text.reverse.foldLeft(BigInt(0)) { (acc, v) =>
    val score = v match {
      case '(' => 1
      case '[' => 2
      case '{' => 3
      case '<' => 4
    }
    acc * 5 + score
  }

def solve10_2(inputs: Vector[String]): BigInt =
  val scores = inputs.flatMap { v =>
    parse(v) match
      case Right(text) =>
        Some(scoreOfAutocomplete(text))
      case _ =>
        None
  }
  scores.sorted.toVector(scores.length / 2)

@main def solve10(): Unit =
  val in = new FileInputStream("example10-2.in")
  System.setIn(in)
  val inputs = Iterator.continually(StdIn.readLine())
    .takeWhile(line => null != line && line.trim.nonEmpty)
    .toVector
  println(solve10_1(inputs))
  println(solve10_2(inputs))