https://adventofcode.com/2016/day/2

bathroomSecurity.sc

val keypad: Seq[Seq[Int]] = Seq(Seq(1, 2, 3), Seq(4, 5, 6), Seq(7, 8, 9))

case class Pos(row: Int, col: Int)

sealed trait Dir
case object Up extends Dir
case object Left extends Dir
case object Right extends Dir
case object Down extends Dir

def move(pos: Pos, dir: Dir): Pos = (pos, dir) match {
  case (Pos(0, _), Up) | (Pos(2, _), Down) |
       (Pos(_, 0), Left) | (Pos(_, 2), Right) => pos

  case (Pos(row, col), Up)    => Pos(row - 1, col)
  case (Pos(row, col), Down)  => Pos(row + 1, col)
  case (Pos(row, col), Left)  => Pos(row, col - 1)
  case (Pos(row, col), Right) => Pos(row, col + 1)
}

def walk(pos: Pos, dirs: Seq[Dir]): Pos = dirs.foldLeft(pos)(move)

def parseInstruction: Char => Dir = {
  case 'U' => Up
  case 'L' => Left
  case 'R' => Right
  case 'D' => Down
}

def parseInstructions(instructions: String): Seq[Seq[Dir]] = {
  instructions.lines.map(_.map(parseInstruction)).toVector
}

def solve(instructions: String): Seq[Int] = {
  val positions = parseInstructions(instructions).scanLeft(Pos(1, 1))(walk)
  positions.tail.map(pos => keypad(pos.row)(pos.col))
}

val instructions =
  """|ULL
     |RRDDD
     |LURDL
     |UUUUD"""
    .stripMargin

solve(instructions)

Alternative solution in Kotlin: https://gist.github.com/paplorinc/0d1942f07788a6b3782b5338d30aa367