There are three types of edits that can be performed on strings: insert a character, remove a character, or replace a character.

OneAway.scala

import org.scalatest.{Matchers, WordSpec}

import scala.annotation.tailrec

/**
  * There are three types of edits that can be performed on strings: insert a character, remove a character,
  * or replace a character.
  * Given two strings, write a function to check if they are one edit (or zero edits) away.
  * pale, pIe -> true
  * pales, pale -> true
  * pale, bale -> true
  * pale, bake -> false
  * Time complexity - O(n+n)=> O(n)
  * Created by Arun Sethia on 7/6/18.
  */
trait OneAwayChar {

  /**
    * find oneaway using Boolean list
    * @param in1
    * @param in2
    * @return
    */
  def oneAway1(in1: String, in2: String): Boolean = {
    val chars: Array[Boolean] = Array.ofDim[Boolean](128)
    in1.foreach(c => {
      chars(c.toInt) = true
    })
    @tailrec
    def isAnyThingAway(newData: List[Char], away: List[Boolean]): Boolean = {
      if (away.length > 1) false
      else {
        newData match {
          case Nil => away.size <= 1
          case h :: _ => {
            val exist = chars(h.toInt)
            if (!exist) {
              isAnyThingAway(newData.tail, exist :: away)
            } else {
              isAnyThingAway(newData.tail, away)
            }
          }
        }
      }
    }
    isAnyThingAway(in2.toList, Nil)
  }

  /**
    * find oneaway using count away
    * @param in1
    * @param in2
    * @return
    */
  def oneAway2(in1: String, in2: String): Boolean = {
    val chars: Array[Boolean] = Array.ofDim[Boolean](128)
    for (c <- in1.toList)
      chars(c.toInt) = true
    @tailrec
    def isAnyThingAway(newData: List[Char], away: Int): Boolean = {
      if (away > 1) false
      else {
        newData match {
          case Nil => away <= 1
          case h :: _ => {
            val exist = chars(h.toInt)
            if (!exist) {
              isAnyThingAway(newData.tail, away + 1)
            } else {
              isAnyThingAway(newData.tail, away)
            }
          }
        }
      }
    }
    isAnyThingAway(in2.toList, 0)
  }
}

/**
  * test cases for OneAwayChar functions
  * Created by Arun Sethia on 5/21/18.
  */
class OneAwaySpec extends WordSpec
  with Matchers
  with OneAwayChar {

  "pale" should {
    "s removed from pales" in {
      assert(oneAway1("pales", "pale"))
    }
  }

  "pales" should {
    "added s in pale" in {
      assert(oneAway1("pale", "pales"))
    }
  }

  "pales" should {
    "replaced p in bale" in {
      assert(oneAway1("pale", "bale"))
    }
  }

  "bake" should {
    "added b k in pale and p l removed" in {
      assert(!oneAway1("pale", "bake"))
    }
  }

  "using away2 pale" should {
    "s removed from pales" in {
      assert(oneAway2("pales", "pale"))
    }
  }

  "using away2 pales" should {
    "added s in pale" in {
      assert(oneAway2("pale", "pales"))
    }
  }

  "using away2 bake" should {
    "added b k in pale and p l removed" in {
      assert(!oneAway2("pale", "bake"))
    }
  }
}