Advent of Code 2021-3.scala

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

def flip(inputs: Vector[Char]): Vector[Char] =
  inputs.map { v => if v == '0' then '1' else '0' }

def binaryToInt(binary: Vector[Char]): Int =
  Integer.parseInt(binary.mkString(""), 2)

def solve3_1(inputs: Vector[String]): Int = {
  val gammaRate = inputs.transpose.map { arr =>
    if (arr.count('0' == _) < arr.count('1' == _)) '1' else '0'
  }
  val epsilonRate = flip(gammaRate)
  binaryToInt(gammaRate) * binaryToInt(epsilonRate)
}

def bitCriteriaOfOxygenGeneratorRating(inputs: Vector[Char]): Char = {
  if inputs.count('0' == _) <= inputs.count('1' == _) then '1' else '0'
}

def bitCriteriaOfCo2ScrubberRating(inputs: Vector[Char]): Char = {
  if inputs.count('0' == _) <= inputs.count('1' == _) then '0' else '1'
}

@tailrec
def findLifeSupportRating(inputs: Vector[String], bitCriteria: Vector[Char] => Char, index: Int = 0): Int = {
  if 1 == inputs.size then
    binaryToInt(inputs.head.toVector)
  else
    val criteriaBit = bitCriteria(inputs.transpose.toVector(index))
    val nexInputs = inputs.filter(_(index) == criteriaBit)
    findLifeSupportRating(nexInputs, bitCriteria, index + 1)
}

def solve3_2(inputs: Vector[String]): Int = {
  val oxygenGeneratorRating = findLifeSupportRating(inputs, bitCriteriaOfOxygenGeneratorRating)
  val co2ScrubberRating = findLifeSupportRating(inputs, bitCriteriaOfCo2ScrubberRating)
  oxygenGeneratorRating * co2ScrubberRating
}

@main def solve3(): Unit =
  val in = new FileInputStream("example3-2.in")
  System.setIn(in)
  val inputs = Iterator.continually(StdIn.readLine())
    .takeWhile(line => null != line && line.trim.nonEmpty)
    .toVector
  println(solve3_1(inputs))
  println(solve3_2(inputs))