Implement an algorithm to determine if a string has all unique characters.

UniqueCharacters.scala

import scala.annotation.tailrec

/**
  * find given string has unique characters
  *
  * Created by Arun Sethia on 5/21/18.
  */
trait UniqueCharacters {
  //ASCII Characters 128
  def isUnique(input: String): Boolean = {
  val ascii: Array[Boolean] = Array.ofDim[Boolean](128)
    @tailrec
    def uniqueness(chars: List[Char],returnValue:Boolean): Boolean = {
      chars match {
        case Nil => returnValue
        case h :: _ => {
          val charIndex = h.toInt
          if (ascii(charIndex)) {
            uniqueness(Nil,false)
          }
          else {
            ascii(charIndex) = true
            uniqueness(chars.tail,true)
          }
        }
      }
    }
    uniqueness(input.toList,false)
  }
}