Aoc2021-day3.scala

package lascala.aoc2021.day1_10.day3

case class DiagnosticReport(
    width: Int,
    bits: Seq[BigInt],
)

extension (bits: Seq[BigInt])
  def mostCommonBit(index: Int): Boolean =
    bits.map(_.testBit(index)).count(_ == true) * 2 >= bits.size

extension (d: DiagnosticReport)
  def buildByPositionBit(f: Int => Boolean): BigInt =
    val bitSeq = for (i <- 0 until d.width) yield if f(i) then '1' else '0'
    BigInt(bitSeq.reverse.mkString, 2)
  def gamma: BigInt            = buildByPositionBit(d.bits.mostCommonBit(_))
  def epsilon: BigInt          = buildByPositionBit(!d.bits.mostCommonBit(_))
  def powerComsumption: BigInt = gamma * epsilon

  def chooseByIterativeFiltering(
      filter: (Int, Seq[BigInt]) => Seq[BigInt],
  ): BigInt =
    @annotation.tailrec
    def loop(index: Int, bits: Seq[BigInt]): BigInt =
      if bits.size == 1 then bits.head
      else loop(index - 1, filter(index, bits))
    loop(d.width - 1, d.bits)
  
  def oxygen: BigInt = chooseByIterativeFiltering { (index, bits) =>
    val mostCommon = bits.mostCommonBit(index)
    bits.filter(_.testBit(index) == mostCommon)
  }
  def co2: BigInt = chooseByIterativeFiltering { (index, bits) =>
    val leastCommon = !bits.mostCommonBit(index)
    bits.filter(_.testBit(index) == leastCommon)
  }
  def lifeSupporting: BigInt = oxygen * co2
end extension

object DiagnosticReport:
  def parse(s: String): DiagnosticReport =
    val lines = s.split("\n")
    DiagnosticReport(
      width = lines.head.size,
      bits = lines.map { line => BigInt(line, 2) },
    )

def solve1(s: String): BigInt = DiagnosticReport.parse(s).powerComsumption

def solve2(s: String): BigInt = DiagnosticReport.parse(s).lifeSupporting

@main def part1: Unit =
  val ans = solve1(input)
  println(ans)

@main def part2: Unit =
  val ans = solve2(input)
  println(ans)

//val input = """111111010011

Aoc2021-day3Test.scala

package lascala.aoc2021.day1_10.day3

import minitest.SimpleTestSuite
import hedgehog.minitest.HedgehogSupport
import hedgehog.*

object Day3Test extends SimpleTestSuite with HedgehogSupport:
  val exampleInput: String = """00100
11110
10110
10111
10101
01111
00111
11100
10000
11001
00010
01010"""

  example("day3 - gammaRate") {
    val d = DiagnosticReport.parse(exampleInput)
    d.gammaRate.toString(2) ==== "10110"
  }

  example("day3 - epsilonRate") {
    val d = DiagnosticReport.parse(exampleInput)
    d.epsilonRate ==== 9
  }

  example("day3 - oxygen") {
    val d = DiagnosticReport.parse(exampleInput)
    d.oxygen ==== 23
  }

  example("day3 - co2") {
    val d = DiagnosticReport.parse(exampleInput)
    d.co2 ==== 10
  }

  example("day3 - solve1") {
    solve1(exampleInput) ==== 198
  }

  example("day3 - solve2") {
    solve2(exampleInput) ==== 230
  }