Euler04.scala

object Euler11 {

  def collect(grid: Array[Array[Int]], x: Int, y: Int, dx: Int, dy: Int, l: Int, acc: Seq[Int]): Seq[Int] =
    if (l <= 0 || x < 0 || y < 0 || y >= grid.length || x >= grid(y).length) acc
    else collect(grid, x + dx, y + dy, dx, dy, l - 1, grid(y)(x) +: acc)

  def chains(grid: Array[Array[Int]], l: Int): Seq[Seq[Int]] =
    for {
      (dx, dy) <- Seq((1, 0), (0, 1), (1, 1), (-1, 1))
      y0 <- 0 until grid.length
      x0 <- 0 until grid(y0).length
      chain = collect(grid, x0, y0, dx, dy, l, Seq())
      if chain.length == l
    } yield chain

  def largestProductInGrid(grid: Array[Array[Int]], length: Int): Int =
    chains(grid, length).map(_.product).sorted.last
}