Matrix Diagonals.scala

import scala.annotation.tailrec

// A lil class to make the code neater
case class Coordinate(x: Int, y: Int)

@tailrec
def diagonal(matrix: List[List[Int]], coordinate: Coordinate, previousPath: List[Int] = List.empty)
  : List[Int] = {
  val path            = previousPath :+ matrix(coordinate.y)(coordinate.x)
  val nextCoordinates = Coordinate(coordinate.x + 1, coordinate.y + 1)

  if (nextCoordinates.y >= matrix.length || nextCoordinates.x >= matrix.head.length) {
    path
  } else {
    diagonal(matrix, nextCoordinates, path)
  }
}

val input = List(
  List(1, 2, 3),
  List(4, 5, 6),
  List(7, 8, 9),
)

// Assumes the lists are all equal length, mmmm lack of type safety
val height = input.length
val width  = input.head.length

// Each range is all the X and Y coordinates respectively, which become the starting points
val topRowStarting     = Range(0, input.head.length).map(x => Coordinate(x, 0)).toSet
val leftColumnStarting = Range(0, input.length).map(y => Coordinate(0, y)).toSet

// Using the Set to de-duplicate the (0, 0) coordinate they both generate
val startingPoints = topRowStarting ++ leftColumnStarting

val diagonals = startingPoints.map(coordinate => diagonal(input, coordinate))