return list/set of pairs of Ints equaling a particular SUM

package org.geo.scala.fundamentals.examples.numerical
import scala.collection.mutable._
/**
 * @author george
 * This class will find the number of unique pairs that equal
 * to some input sum in an input array
 *
 * @param a    Int array containing numbers to look for pairs in
 * @param n    Int sum we are trying to find in a
 *
 */
class PairsSummingToN(val a: Array[Int], val n: Int) {
  require(n > 0)
  require(a.length > 1)

  /**
 * @return list of pairs that may contain duplicates
 */
def getPairsEqualingToSumList(): ListBuffer[(Int, Int)] = {
    val listOfPairs = new ListBuffer[(Int, Int)]()
    val map: Map[Int, ListBuffer[Int]] = new HashMap[Int, ListBuffer[Int]]()
    a.indices.foreach(i => {
      val x = -(a(i) - n)
      val m = map get x
      if (m == None) {
        /** put a new map entry into the value of map **/
        map += (x -> ListBuffer(i))
      } else {
        /** get the map out and update it **/
        val mi = m.get
        mi += (i)
      }
      val f = map get a(i)
      if (f != None) {
        val lb = f.get
        listOfPairs += ((a(i), a(f.get.apply(f.get.size - 1))))
      }
    })
    listOfPairs
  }

  /**
 * @return A unique set of pairs without duplicates
 */
def getPairsEqualingToSumSet(): Set[(Int, Int)] = {
    val setOfPairs = new HashSet[(Int, Int)]()
    val map: Map[Int, ListBuffer[Int]] = new HashMap[Int, ListBuffer[Int]]()
    a.indices.foreach(i => {
      val x = -(a(i) - n)
      val m = map get x
      if (m == None) {
        /** put a new List into the value of map **/
        map += (x -> ListBuffer(i))
      } else {
        /** get the list out and update it **/
        val mi = m.get
        mi += (i)
      }
      val f = map get a(i)
      if (f != None) {
        val lb = f.get
        setOfPairs += ((a(i), a(f.get.apply(f.get.size - 1))))
      }
    })
    setOfPairs
  }
}

object PairsSummingToN {

  def getPairs(tyP: Boolean)(a: Array[Int], n: Int) = {
    val solutionSet = new PairsSummingToN(a, n)
    tyP match {
      case true  => solutionSet.getPairsEqualingToSumList()
      case false => solutionSet.getPairsEqualingToSumSet()
    }
  }
}