Stable marriage implementation in Scala (#460)

* stable marrige implementation in scala

* refactor implementation details out of main

* change from a ListBuffer to a Queue for bachelors

Author: kenpower

Diff for: contents/stable_marriage_problem/code/scala/stable_marriage.scala

@@ -0,0 +1,65 @@
+import scala.collection.mutable._
+
+object StableMarriage {
+
+  var bachelors = Queue[Man]()
+
+  case class Man(name: String, var preferences: List[Woman] = List()) {
+    def propose(): Unit = preferences match {
+      case woman :: remainingPreferences => {
+        if (woman.prefers(this)) {
+          bachelors ++= woman.fiance
+          woman.fiance = Some(this)
+        }
+        else
+          bachelors.enqueue(this)
+        preferences = remainingPreferences
+      }
+      case _ =>
+    }
+  }
+
+  case class Woman(name: String, var preferences: List[Man] = List(), var fiance: Option[Man] = None) {
+    def prefers(man: Man): Boolean =
+      fiance match {
+        case Some(otherMan) => preferences.indexOf(man) < preferences.indexOf(otherMan)
+        case _ => true //always prefer any man over nobody
+      }
+  }
+
+  def findStableMatches(men: Man*): Unit = {
+    bachelors = men.to[Queue]
+    while (bachelors.nonEmpty)
+      bachelors.dequeue.propose()
+  }
+}
+
+object StableMarriageExample {
+
+  val a = StableMarriage.Man("Adam")
+  val b = StableMarriage.Man("Bart")
+  val c = StableMarriage.Man("Colm")
+  val x = StableMarriage.Woman("Xena")
+  val y = StableMarriage.Woman("Yeva")
+  val z = StableMarriage.Woman("Zara")
+
+  a.preferences = List(y, x, z)
+  b.preferences = List(y, z, x)
+  c.preferences = List(x, z, y)
+  x.preferences = List(b, a, c)
+  y.preferences = List(c, a, b)
+  z.preferences = List(a, c, b)
+
+
+  def main(args: Array[String]): Unit = {
+
+    StableMarriage.findStableMatches(a, b, c)
+
+    List(x, y, z).foreach(
+      w => Console.println(
+        w.name
+          + " is married to "
+          + w.fiance.getOrElse(StableMarriage.Man("Nobody")).name))
+  }
+
+}

Diff for: contents/stable_marriage_problem/stable_marriage_problem.md

@@ -46,6 +46,8 @@ I am incredibly interested to see what you guys do and how you implement the alg
 [import, lang:"java"](code/java/stable-marriage.java)
 {% sample lang="php" %}
 [import, lang:"php"](code/php/stable_marriage.php)
+{% sample lang="scala" %}
+[import, lang:"scala"](code/scala/stable_marriage.scala)
 {% endmethod %}
 
 <script>