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  1. import scala.collection.mutable
  2.  
  3. class Index[K, V](fn: V => K) {
  4.   private val elements = new mutable.HashMap[K, mutable.Set[V]] with mutable.MultiMap[K, V]
  5.  
  6.   def +=(element: V) = {
  7.     val key = fn(element)
  8.     elements.addBinding(key, element)
  9.   }
  10.  
  11.   def -=(element: V) = {
  12.     val key = fn(element)
  13.     elements.removeBinding(key, element)
  14.   }
  15.  
  16.   def get(key: K): Set[V] =
  17.     elements.get(key).map(_.toSet) getOrElse Set.empty
  18. }
  19.  
  20. trait IndexedSet[V] extends mutable.Set[V] {
  21.   private val indices = mutable.ListBuffer.empty[Index[_, V]]
  22.  
  23.   def addIndex[K](fn: V => K): Index[K, V] = {
  24.     val index = new Index(fn)
  25.     for (elem <- this) {
  26.       index += elem
  27.     }
  28.     indices += index
  29.     index
  30.   }
  31.  
  32.   abstract override def +=(elem: V) = {
  33.     for (index <- indices) {
  34.       index += elem
  35.     }
  36.     super.+=(elem)
  37.   }
  38.  
  39.   abstract override def -=(elem: V) = {
  40.     for (index <- indices) {
  41.       index -= elem
  42.     }
  43.     super.-=(elem)
  44.   }
  45. }
  46.  
  47. object Main extends App {
  48.   val set = new mutable.HashSet[Int] with IndexedSet[Int]
  49.   val index = set.addIndex(_ % 2 == 0)
  50.   for (i <- 1 to 20) {
  51.     set += i
  52.   }
  53.   println(index.get(true))
  54.   println(index.get(false))
  55. }
Success #stdin #stdout 0.42s 322240KB
comments (?)
stdin 
Standard input is empty
stdout 
Set(10, 14, 20, 6, 2, 12, 18, 16, 8, 4)
Set(5, 1, 9, 13, 17, 7, 3, 11, 19, 15)
https://ideone.com/2g95ys
language:
Scala (scala 2.12.8)
created:
9 years ago
visibility:
secret

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