scala.collection.mutable

// first import all necessary types from package `collection.mutable`
import collection.mutable.{ HashMap, MultiMap, Set }
// to create a `MultiMap` the easiest way is to mixin it into a normal
// `Map` instance
val mm = new HashMap[Int, Set[String]] with MultiMap[Int, String]
// to add key-value pairs to a multimap it is important to use
// the method `addBinding` because standard methods like `+` will
// overwrite the complete key-value pair instead of adding the
// value to the existing key
mm.addBinding(1, "a")
mm.addBinding(2, "b")
mm.addBinding(1, "c")
// mm now contains `Map(2 -> Set(b), 1 -> Set(c, a))`
// to check if the multimap contains a value there is method
// `entryExists`, which allows to traverse the including set
mm.entryExists(1, _ == "a") == true
mm.entryExists(1, _ == "b") == false
mm.entryExists(2, _ == "b") == true
// to remove a previous added value there is the method `removeBinding`
mm.removeBinding(1, "a")
mm.entryExists(1, _ == "a") == false

val pq = collection.mutable.PriorityQueue(1, 2, 5, 3, 7)
println(pq)                  // elements probably not in order
println(pq.clone.dequeueAll) // prints ArraySeq(7, 5, 3, 2, 1)