Hackerrank `Migratory Birds` problem

MigratoryBirds.scala

// https://www.hackerrank.com/challenges/migratory-birds/problem
//
//          Input             Output
// +-----------------------+----------+
// | 6                     |     4    |
// | 1 4 4 4 5 3           |          |
// +-----------------------+----------+
// | 11                    |     3    |
// | 1 2 3 4 5 4 3 2 1 3 4 |          |
// +-----------------------+----------+

import scala.io._

object MigratoryBirds {
  def migratoryBirds(arr: Array[Int]): Int = arr.foldLeft(Array(0, 0, 0, 0, 0), 0)((acc, el) => {
    val sightingsLog = acc._1
    val mostCommonBird = acc._2

    if(mostCommonBird == 0) {
      sightingsLog(el - 1) = 1
      (sightingsLog, el)
    } else {
      val sightingsOfGivenSpecies = sightingsLog(el - 1) + 1
      val sightingsOfMostCommonBird = sightingsLog(mostCommonBird - 1)
      
      sightingsLog(el - 1) = sightingsOfGivenSpecies
      val newMostCommonBird = 
        if (sightingsOfGivenSpecies > sightingsOfMostCommonBird) el
        else if(sightingsOfGivenSpecies == sightingsOfMostCommonBird && el < mostCommonBird) el
        else mostCommonBird
      (sightingsLog, newMostCommonBird)
    }
  })._2

  def main(args: Array[String]): Unit = {
    val arrCount = StdIn.readLine.trim.toInt

    val arr = StdIn.readLine.replaceAll("\\s+$", "").split(" ").map(_.trim.toInt)
    val result = migratoryBirds(arr)

    println(result)
  }
}