Created
October 23, 2012 22:13
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Functional programming course at Coursera week 6.
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| package forcomp | |
| import common._ | |
| object Anagrams { | |
| type Word = String | |
| type Sentence = List[Word] | |
| type Occurrences = List[(Char, Int)] | |
| val dictionary: List[Word] = loadDictionary | |
| def wordOccurrences(w: Word): Occurrences = | |
| w.toList.groupBy(_.toLower).map(_ match {case (a,b) => (a, b.length)}).toList.sortWith(_._1 < _._1) | |
| def sentenceOccurrences(s: Sentence): Occurrences = s match { | |
| case Nil => Nil | |
| case x :: xs => s.map(wordOccurrences(_)).reduce(_++_).groupBy(_._1).map(_ match { | |
| case (c,xs) => (c, xs.map(_._2).sum) | |
| }).toList.sortWith(_._1 < _._1) | |
| } | |
| lazy val dictionaryByOccurrences: Map[Occurrences, List[Word]] = | |
| dictionary.groupBy(wordOccurrences(_)) | |
| def wordAnagrams(word: Word): Iterable[Word] = | |
| dictionaryByOccurrences.get(wordOccurrences(word)).flatten | |
| def combinations(xs: Occurrences): List[Occurrences] = xs match { | |
| case Nil => List(Nil) | |
| case (_,0) :: ys => combinations(ys) | |
| case (c,n) :: ys => combinations((c,n-1) :: ys) ++ combinations((c,n-1) :: ys).map(zs => | |
| zs.find(_._1 == c) match { | |
| case Some(_) => zs.map(_ match { | |
| case (d, o) => if (d == c) (d,o+1) else (d, o) | |
| }) | |
| case None => (c,1) :: zs | |
| }) | |
| } | |
| def subtract(xs: Occurrences, ys: Occurrences): Occurrences = | |
| xs.map(x => ys.find(_._1 == x._1) match { | |
| case Some(y) => (x._1, x._2 - y._2) | |
| case None => x | |
| }).filter(_._2 != 0) | |
| def sentenceAnagrams(s: Sentence): List[Sentence] = { | |
| def h(xs: Occurrences): Iterable[Word] = dictionaryByOccurrences.get(xs).flatten | |
| def f(xs: Occurrences): List[Sentence] = xs match { | |
| case Nil => List(Nil) | |
| case _ => combinations(xs) flatMap (c => h(c) flatMap (w => f(subtract(xs,c)).map(w :: _))) | |
| } | |
| f(sentenceOccurrences(s)) | |
| } | |
| } |
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Does not work !