Googlander.scala

object Googlander extends App {

  lazy val memo = collection.mutable.Map.empty[(Int, Int), Long]

  def countPaths(r: Int)(c: Int): Long = memo.getOrElseUpdate(
    (r, c),
    if (c <= 1) 1 else (1 to r map countPaths(c - 1)).sum
  )

  def process(lineIn: Iterator[String])(lineOut: String => Unit) =
    for (i <- 1 to lineIn.next().toInt) {
      val Array(r, c) = lineIn.next().split(' ').map(_.toInt)
      lineOut(s"Case #$i: ${countPaths(r)(c)}")
    }

  val filename = "D-large-practice"
  val writer = new java.io.PrintWriter(filename + ".out")
  try {
    process(io.Source.fromFile(filename + ".in").getLines) { s =>
      writer.println(s); writer.flush()
    }
  } finally {
    writer.flush(); writer.close()
  }
}

GooglanderTest.scala

import org.scalatest._

import Googlander._

class GooglanderTest  extends FunSuite {

  test("sample #1") {
    assert(countPaths(1)(1) === 1)
  }

  test("sample #2") {
    assert(countPaths(1)(3) === 1)
  }

  test("sample #3") {
    assert(countPaths(3)(3) === 6)
  }

  test("2 x 3") {
    assert(countPaths(2)(3) === countPaths(2)(1) + countPaths(2)(2))
  }

  test("sample case") {
    val input = """3
1 1
1 3
3 3""".lines

    val expected = """Case #1: 1
Case #2: 1
Case #3: 6""".lines

    lineComparison(input, expected)
  }
  
  test("full small case") {
    val input = io.Source.fromFile("D-small-practice.in").getLines()
    val expected = io.Source.fromFile("D-small-practice.out").getLines()

    lineComparison(input, expected)
  }

  test("full large case") {
    val input = io.Source.fromFile("D-large-practice.in").getLines()
    val expected = io.Source.fromFile("D-large-practice.out").getLines()

    lineComparison(input, expected)
  }

  def lineComparison(input: Iterator[String], expected: Iterator[String]) {
    process(input) { s =>
      for (line <- s.lines) assert(line.trim === expected.next().trim)
    }
    assert(expected.hasNext === false, "Finished too fast.")
  }

}