advent of code - day15

day15.scala

package day15

import day15.Day15.{Memory, solve}

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

object Day15:

  case class Memory(dict: Map[Int, Int] = Map.empty, lastSpoken: Int = -1)

  @tailrec
  def solve(starting: Array[Int], goal: Int, memory: Memory = new Memory(), turn: Int = 1): Int = {
    val lastSpoken = memory.lastSpoken
    val dict = memory.dict
    val nextTurn = turn + 1
    turn match {
      case _ if (turn > goal) => lastSpoken
      case x if x <= starting.length => {
        val speak = starting(turn - 1)
        solve(starting, goal, Memory(dict.updated(lastSpoken, turn), starting(turn - 1)), nextTurn)
      }
      case _ => {
        if (dict.contains(lastSpoken)) {
          val speak = turn - dict.get(lastSpoken).get
          solve(starting, goal, Memory(dict.updated(lastSpoken, turn), speak), nextTurn)
        } else {
          solve(starting, goal, Memory(dict.updated(lastSpoken, turn), 0), nextTurn)
        }
      }
    }
  }

  @main def solve15_1() =
    val in = new FileInputStream("src/example15-1.in")
    System.setIn(in)
    val inputs = StdIn.readLine().split(",").map(_.toInt)
    println(solve(inputs, 2020))
    println(solve(inputs, 30000000))
  

Day15Test.scala

package day15

import org.junit.Assert._
import org.junit.Test

class Day15Test {
  @Test def test(): Unit = {
    assertEquals(1, Day15.solve(Array(1, 3, 2), 2020))
    assertEquals(436, Day15.solve(Array(0, 3, 6), 2020))
    assertEquals(27, Day15.solve(Array(1, 2, 3), 2020))
    assertEquals(78, Day15.solve(Array(2, 3, 1), 2020))
    assertEquals(438, Day15.solve(Array(3, 2, 1), 2020))
    assertEquals(1836, Day15.solve(Array(3, 1, 2), 2020))
  }
}