Vowel Families

vowel_families.worksheet.sc

/**
  * Given two words, we can determine if they have the same vowels, 
  * ignoring order and repetition. 
  * 
  * For instance, “Hello” and “Vowel” both have \e and \o, so they have the same vowels. 
  * 
  * Write a function that groups words into “families” that all have the same vowels. 
  * “Tree” and “tent” also belong to the same family because we ignore the repetition of \e.
  * 
  * Examples
  * 
  * (vowel-families ["hello" "vowel" "fox" "cot" "hat" "cat"]) ;=> [["hello" "vowel"]
                                                               ;    ["fox" "cot"]
                                                               ;    ["hat" "cat"]]
    (vowel-families []) ;=> []
    (vowel-families ["tree" "tent" "blanket"] ;=> [["tree" "tent"]
                                              ;    ["blanket"]]
  * 
  * Notes
  * 
  * For this exercise, the vowels are \a, \e, \i, \o, and \u. 
  * If you wish, you may include vowels from other languages and scripts. 
  * Your algorithm should not be case-sensitive.
  * 
  * Please maintain capitalization and non-alphabetic characters.
  */

import $scalac.`-Ypartial-unification`
import $dep.`org.typelevel::cats-core:2.3.0`

import cats.data.State
import cats.implicits._

import scala.collection.immutable._

def isVowel(c: Char): Boolean =
  "AEIOUaeiou".indexOf(c) =!= -1

def vowels(str: String): Set[Char] =
  str.toSet.filter(isVowel)

type Acc = Map[Set[Char], List[String]]

def f(str: String): State[Acc, Unit] = {
  State { acc =>
    val vwls = vowels(str)

    val family = acc.get(vwls) match {
      case Some(fam) => str :: fam
      case None => List(str)
    }

    val newAcc = acc + (vwls -> family)

    (newAcc, ())
  }
}

def vowelFamilies(words: List[String]) =
  words
    .traverse_(f)
    .run(initialState)
    .value
    ._1

val initialState: Acc = Map.empty[Set[Char], List[String]]

vowelFamilies(List.empty[String])
vowelFamilies(List("hello", "vowel"))
vowelFamilies(List("tree", "tent", "blanket"))