Design a stack which, in addition to push and pop, has a function min which returns the minimum element.

MinStack.scala

/**
  * Design a stack which, in addition to push and pop, has a function min which returns the minimum element.
  * Push, pop and min should all operate in 0(1) time.
  * Created by Arun Sethia on 7/29/18.
  */
case class MinStack(data: List[Int], min: Int) {
  /**
    *
    * @param elem
    * @return
    */
  def push(elem: Int) = {
    val (dataAdd, minimum) = findMinimumAndData(elem, min)
    MinStack(dataAdd :: data, minimum)
  }

  /**
    * find new data and minimum
    *
    * @param newData
    * @param currentMin
    * @return
    */
  def findMinimumAndData(newData: Int, currentMin: Int): (Int, Int) = {
    if (min == 0) (newData, newData)
    else if (newData > min) (newData, currentMin)
    else ((newData - currentMin), newData)
  }

  /**
    *
    * @return
    */
  def pop() = data match {
    case h :: _ => {
      val (poppedItem, newMin) = if (h < min) (min, (min - h)) else (h, min)
      println(s"pop:: ${poppedItem} and new minimum:${newMin}")
      MinStack(data.tail, newMin)
    }
    case Nil => throw new UnsupportedOperationException("stack is empty")
  }

  override def toString() = s"Minimum:${min}"
}