Solutions for HackerRank Interview

solutions.scala

// derived this formula for summation of odd integers
def calculate(arr: Array[Int]) = {
  arr.map{
    (days) =>
      val numOddPairs = Math.round((days - 1).toDouble / 4)
      val numOddNumbers = Math.ceil(days.toDouble / 2).toInt
      val midPoint = days match {
        case _ => if (numOddNumbers % 2 == 1) Math.ceil(days.toDouble / 2).toInt else 0
      }

      2 * Math.round((days + 1) / 2) * numOddPairs + midPoint
  }
}

calculate((1 to 10).toArray)

//res0: Array[Long] = Array(1, 1, 4, 4, 9, 9, 16, 16, 25, 25)

def customSort(arr: Array[Int]) = {
  arr.groupBy(identity).mapValues(_.length).toList.sortBy(x => x._2 -> x._1).flatMap {
    case (num, freq) => List.fill(freq)(num)
  }
}

customSort(Array(3, 1, 2, 2, 4))

// res2: List[Int] = List(1, 3, 4, 2, 2)

def calculate_amount(arr: Array[Int]) : Long = {
  def costFn(cost: Long, discount: Long) : Long = if (discount > cost) 0 else cost - discount
  if (arr.length == 0) 0 else
    arr.foldLeft((Long.MaxValue, 0.toLong)){
      case ((currMin, total), elem) => (Math.min(currMin, elem),
        total.toLong + costFn(elem.toLong, Math.min(elem, currMin)))
    }._2 + arr.head.toLong
}

calculate_amount(Array(4, 9, 2, 3))
calculate_amount(Array(1, 2, 3, 4))

//res5: Long = 10
//res6: Long = 7


def kSub(k: Int, nums: Array[Int]): Long = {
  nums.scanLeft(0)(_ + _).map(_ % k).groupBy(identity).mapValues(_.length).values.map(x => x * (x - 1) / 2).sum
}

kSub(3, Array(1, 2, 3, 4, 1))
kSub(2, Array(1, 2, 1, 2, 1, 2))