advent-of-code-2019

2.scala

import scala.io.Source

var TAPE = Array.empty[Int]

// Instructions
val OP_ADD = 1
val OP_MUL = 2
val OP_END = 99

// Instruction Pointer
var TAPE_POS = 0

def add(): Int = {
  val ADR_A = TAPE(TAPE_POS + 1) // Noun
  val ADR_B = TAPE(TAPE_POS + 2) // Verb
  val ADR_O = TAPE(TAPE_POS + 3)

  TAPE(ADR_O) = TAPE(ADR_A) + TAPE(ADR_B)

  3
}

def mult(): Int = {
  val ADR_A = TAPE(TAPE_POS + 1) // Noun
  val ADR_B = TAPE(TAPE_POS + 2) // Verb
  val ADR_O = TAPE(TAPE_POS + 3)

  TAPE(ADR_O) = TAPE(ADR_A) * TAPE(ADR_B)

  3
}

def doop(op: Int): Int = op match {
  case OP_ADD => add()
  case OP_MUL => mult()
  case OP_END => 0
}

def readprog() = {
  println("TAPE has size " + TAPE.length)
  println("Initial Program State: "+ TAPE.mkString(","))
  println("--")

  var CUR_OP = -1
  while (CUR_OP != OP_END) {
    CUR_OP = TAPE(TAPE_POS)

    val params = doop(CUR_OP)
    TAPE_POS += (params + 1)
  }

  println("Final Program State: " + TAPE.mkString(","))
}

def resetprog() = {
  TAPE = Source.fromFile("input.txt").getLines().next.split(",").map(_.toInt)
  TAPE_POS = 0
}

resetprog()
readprog()

val TARGET = 19690720 // Noun + verb
// breadth-first search; assumes value will exist
def findprog(noun : Int, candidates : Vector[Int]) : Int = {
  for (verb <- candidates) {
    resetprog()

    TAPE(1) = noun
    TAPE(2) = verb

    readprog()

    if (TAPE(0) == TARGET) return (100 * noun + verb)
  }

  val rest :+ first = candidates
  findprog(first, rest)
}
val inputs = Vector.range(0, 100)
val candidates :+ noun : Vector[Int] = inputs
val answer = findprog(noun, candidates)

println("Part 2 answer: " + answer)