A collection of string operations using Scala's functional principles.

Strings.scala

object Strings {
  
  def isAnagram(s1: String, s2: String): Boolean = {
    if (s1 == null || s2 == null || s1.length != s2.length) return false
    s1.zip(s2).foldLeft(0){ case (result, (left, right)) => result ^ (left ^ right) } == 0
  }
  
  def isAnagram2(s1: String, s2: String): Boolean = {
    val m1 = s1 groupBy(c => c) mapValues(_.length)
    val m2 = s2 groupBy(c => c) mapValues(_.length)
    (m1 ++ m2).map{ case (k,v) => v - m1.getOrElse(k, 0) }.sum == 0
  }
  
  def isParenthesisBalanced(s: String): Boolean = {
    val openParens = Set('(', '[', '{')
    val closeParens = Set(')', ']', '}')
    val m = closeParens.zip(openParens).toMap
    
    s.toCharArray.foldLeft(List[Char]()){
      case (rs, open) if openParens.contains(open) => open :: rs
      case (r :: rs, closed) if closeParens.contains(closed) && m.get(closed).get == r => rs
      case (rs, closed) if closeParens.contains(closed) => 'x' :: rs
      case (rs, _) => rs
    }.isEmpty
  }
}