CounterCulture.scala

object CounterCulture extends App {

  def minCount(n: Long): Long = minCount(n.toString)

  def minCount(n: String): Long =
    if (n.toLong < 20) n.toLong
    else {
      val (front, back) = n splitAt (n.size + 1) / 2
      val beforeReverse = "1" + "0" * (back.size - 1) + front.reverse
      if (back.toLong == 0) minCount(n.toLong - 1) + 1
      else {
        val train9 = "9" * (n.size - 1)

        minCount(train9) +
          (beforeReverse.toLong - train9.toLong) +
          (back.toLong - 1) +
          (if (beforeReverse == beforeReverse.reverse) 0 else 1)
      }
    }

  def process(lineIn: Iterator[String])(lineOut: String => Unit) =
    for (i <- 1 to lineIn.next().toInt) {
      lineOut(s"Case #$i: ${minCount(lineIn.next())}")
    }

  val filename = "A-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()
  }

}

CounterCultureTest.scala

import org.scalatest._

import CounterCulture._

class CounterCultureTest extends FunSuite {

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

  test("sample #2") {
    assert(minCount(19) === 19)
  }

  test("sample #3") {
    assert(minCount(23) === 15)
  }

  test("21") {
    assert(minCount(21) === 13)
  }

  test("123456") {
    assert(minCount(123456) === minCount(99999) + (100321 - 99999) + (123456 - 123001) + 1)
  }
  
  test("3000") {
    assert(minCount(3000) === (3000 - 2901) + (1092 - 999) + minCount("999") + 1)
  }
  
  test("sample case") {
    val input = """3
1
19
23""".lines

    val expected = """Case #1: 1
Case #2: 19
Case #3: 15""".lines

    lineComparison(input, expected)
  }

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

    lineComparison(input, expected)
  }

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

}