Christmas Coding Challenge 2019 (Scala)

ccc-2019.scala

case class RegexOperator(c:Char,a:Option[Char]=None) {
  def eqmatch(ch:Char): Boolean = ch == c || c == '.'
}
def parsePattern(p:String) =
  p.foldLeft(Seq.empty[RegexOperator])( (agg,el)=> el match {
    case '*' =>agg.init :+ agg.last.copy(a=Some('*'))
    case c => agg :+ RegexOperator(c)
  })

def regex(p:String,s:String): Boolean = {
  def _regex(p:Seq[RegexOperator],s:String): Boolean = {
    if(p.isEmpty && s.isEmpty) true
    else if(p.isEmpty && s.nonEmpty) false
    else {
      p.head match {
        case RegexOperator(_,Some('*')) if s.isEmpty || !p.head.eqmatch(s.head) => _regex(p.tail,s)
        case RegexOperator(_,Some('*')) if p.head.eqmatch(s.head) => _regex(p,s.tail)
        case RegexOperator(_,_) if p.head.eqmatch(s.head) => _regex(p.tail,s.tail)
        case _ => false
      }
    }
  }
  _regex(parsePattern(p),s)
}



Vector(
  (regex("ab","aba"),false),
  (regex("a*","aa"),true),
  (regex(".*","ab"),true),
  (regex(".","ab"),false),
  (regex("c*a*b","aab"),true),
  (regex(".c*a*b","aab"),true),
  (regex("a*","aaa"),true)
).foreach{ w=>
  assert(w._1 == w._2)
}