gistfile1.scala

def words(s: String): Set[String]

def makeWordMap(sentences: List[String]) = {
  val forwardMap = sentences.map(s => (s, words(s))).toMap
  sentences.flatMap(words)
           .distinct
           .map(w => sentences.filter(forwardMap(s)))
}
def makeWordMap2(sentences: List[String]) = {
  val words1 = collection.mutable.Map.empty[String, Set[String]]
  for(sentence <- sentences; word <- words(sentence)){
    words1.getOrElseUpdate(word, Set()) += sentence
  }
  words1
}

def makeWordMap(sentences):
  result = {}
  for sentence in sentences:
    for word in words(sentence):
      if word not in result:
        result[word] = []
      result[word].append(sentence)
  return result
  
def makeWordMap(sentences):
  forwardMap = {s: words(s) for s in sentences}
  return {
    word: filter(forwardMap[s].contains, sentences)
    for s in sentences
    for word in words
  }