最長重複文字列問題

strProblem.scala

def maxDupStr(str:String) = {
  def tails:String => List[String] = {
    case "" => Nil
    case x => x :: tails(x.tail)
  }
  val sorted = tails(str) sorted
  val pair = sorted zip sorted.tail
  val maxPair = {
    pair map { case (s1,s2) => (s1 zip s2 filter {c => c._1 == c._2} size, s1)} max
  }
  maxPair._2 take maxPair._1
}
assert(maxDupStr("abcab") == "ab")
assert(maxDupStr("abcdefgcdef") == "cdef")