StandingOvation.scala

import java.io.FileOutputStream

import scala.io.Source

object StandingOvation {
  val INPUT = "A-large-practice.in"
  val OUTPUT = INPUT.takeWhile(_ != '.') + ".out"

  def minFriends(shyness: String): Int = {

    def loop(currentLevel: Int, total: Int, acc: Int): Int = {
      if (currentLevel >= shyness.size) acc
      else {
        val current = shyness(currentLevel) - '0'
        val acc0 = if (currentLevel < total) 0 else currentLevel - total
        loop(currentLevel + 1, total + current + acc0, acc + acc0)
      }
    }
    loop(0, 0, 0)
  }

  def main(args: Array[String]): Unit = {
    val itr = Source.fromFile(INPUT).getLines()
    val sets = itr.next().toInt

    val writer = new FileOutputStream(OUTPUT)
    //    val writer = Console.out
    try {
      Console.withOut(writer) {
        for (set <- 1 to sets) {
          val Array(_, shyness) = itr.next().split(' ')
          println(f"Case #${set}: ${minFriends(shyness)}")
        }
      }
    } finally {
      writer.flush()
      writer.close()
    }
  }
}

StandingOvationSpec.scala

import org.scalatest.FunSuite
import StandingOvation._

class StandingOvationSpec extends FunSuite {

  test("sample #1") {
    assert(minFriends("11111") === 0)
  }

  test("sample #2") {
    assert(minFriends("09") === 1)
  }

  test("sample #3") {
    assert(minFriends("110011") === 2)
  }

  test("sample #4") {
    assert(minFriends("1") === 0)
  }

}