Project Euler: Problem 28

Euler0028.scala

package euler.zerosum

object Euler0028 {

  def main(args: Array[String]) {
    println(getCorner(3, 1001, from(1).take(1)).sum)
  }

  private def getCorner(width: Int, maxWidth: Int, corners: Stream[Int]): Stream[Int] = {
    val maxValue: Int = maxWidth * maxWidth
    if (corners.last > maxValue) {
      corners.takeWhile(_ <= maxValue)
    } else {
      val nextCorners = from((width - 2) * (width - 2) + 1)
                        .takeWhile(_ <= width * width)
                        .filter(_ % (width - 1) == 1)
      getCorner(width + 2, maxWidth, corners #::: nextCorners)
    }
  }

  private def from(n: Int): Stream[Int] = n #:: from(n + 1)
}