AoC 2017 | day 3 | part 2

aoc2017d3p2.scala

import scala.annotation.tailrec

val input = 347991

type Grid = Map[(Int, Int), Int]
val grid: Grid = Map(
    (0, 0) -> 1,
    (1, 0) -> 1
).withDefaultValue(0)

sealed trait Direction
object Upwards extends Direction
object Downwards extends Direction
object Leftwards extends Direction
object Rightwards extends Direction

def neighborSum(grid: Grid, x: Int, y: Int): Int = {
    List(
        (x - 1, y + 1), (x, y + 1), (x + 1, y + 1),
        (x - 1, y),                 (x + 1, y),
        (x - 1, y - 1), (x, y - 1), (x + 1, y - 1)
    ).map(grid).sum
}

@tailrec
def traverseGrid(grid: Grid, x: Int, y: Int, dir: Direction, level: Int, count: Int, limit: Int): Int = {
    val value = neighborSum(grid, x, y)

    if (value > limit)
        value
    else {
        val updatedGrid = grid + ((x, y) -> value)

        dir match {
            case Upwards =>
                if (count < level * 2 - 2)
                    traverseGrid(updatedGrid, x, y + 1, Upwards, level, count + 1, limit)
                else
                    traverseGrid(updatedGrid, x - 1, y, Leftwards, level, 0, limit)

            case Leftwards =>
                if (count < level * 2 - 1)
                    traverseGrid(updatedGrid, x - 1, y, Leftwards, level, count + 1, limit)
                else
                    traverseGrid(updatedGrid, x, y - 1, Downwards, level, 0, limit)

            case Downwards =>
                if (count < level * 2 - 1)
                    traverseGrid(updatedGrid, x, y - 1, Downwards, level, count + 1, limit)
                else
                    traverseGrid(updatedGrid, x + 1, y, Rightwards, level, 0, limit)

            case Rightwards =>
                if (count < level * 2)
                    traverseGrid(updatedGrid, x + 1, y, Rightwards, level, count + 1, limit)
                else
                    traverseGrid(updatedGrid, x, y + 1, Upwards, level + 1, 0, limit)
        }
    }
}

traverseGrid(grid, 1, 1, Upwards, 1, 0, input)