Advent of Code 08 part 1.scala

import java.io.FileInputStream
import scala.io.StdIn

@main def solve8() =
  case class Instruction(code: String, value: Int)

  def solve(instructions: Vector[Instruction], hitCount: Array[Int], pc: Int = 0, acc: Int = 0): Int = {
    if 1 <= hitCount(pc) then
      acc
    else
      hitCount(pc) += 1
      val instruction = instructions(pc)
      instruction.code match {
      case "acc" =>
        solve(instructions, hitCount, pc + 1, acc + instruction.value)
      case "jmp" =>
        solve(instructions, hitCount, pc + instruction.value, acc)
      case _ =>
        solve(instructions, hitCount, pc + 1, acc)
      }
  }

  val in = new FileInputStream("example8-1.in")
  System.setIn(in)

  val inputs = Iterator.continually(StdIn.readLine()).takeWhile(_ != null).toVector
  val instructions = inputs.map { line =>
    val Array(code, value) = line.trim.split(" ")
    Instruction(code, value.toInt)
  }
  println(solve(instructions, Array.ofDim(instructions.size)))
  

Advent of Code 08 part 2.scala

import java.io.FileInputStream
import scala.io.StdIn

@main def solve8() =
  case class Instruction(code: String, value: Int)

  def run(instructions: Vector[Instruction], hitCount: Array[Int], lastPc: Int = 0, pc: Int = 0, acc: Int = 0): Option[Int] = {
    if instructions.size <= pc then {
      Some(acc)
    } else if 1 <= hitCount(pc) then {
      None
    } else
      hitCount(pc) += 1
      val instruction = instructions(pc)
      instruction.code match {
        case "acc" =>
          run(instructions, hitCount, pc, pc + 1, acc + instruction.value)
        case "jmp" =>
          run(instructions, hitCount, pc, pc + instruction.value, acc)
        case _ =>
          run(instructions, hitCount, pc, pc + 1, acc)
      }
  }

  def solve(instructions: Vector[Instruction]): Int = {
    instructions.indices.toIterable.map { idx =>
      if instructions(idx).code == "jmp" then {
        val patchedInstructions = instructions.updated(idx, instructions(idx).copy(code = "nop"))
        run(patchedInstructions, Array.ofDim(instructions.size))
      } else {
        Option.empty[Int]
      }
    }.find(_.nonEmpty).flatten.getOrElse(0)
  }

  val in = new FileInputStream("example8-1.in")
  System.setIn(in)

  val inputs = Iterator.continually(StdIn.readLine()).takeWhile(_ != null).toVector
  val instructions = inputs.map { line =>
    val Array(code, value) = line.trim.split(" ")
    Instruction(code, value.toInt)
  }
  println(solve(instructions))