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Task/Amb/Scala/amb.scala

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+object Amb {
+
+  def amb(wss: List[List[String]]): Option[String] = {
+    def _amb(ws: List[String], wss: List[List[String]]): Option[String] = wss match {
+      case Nil => ((Some(ws.head): Option[String]) /: ws.tail)((a, w) => a match {
+        case Some(x) => if (x.last == w.head) Some(x + " " + w) else None
+        case None => None
+      })
+      case ws1 :: wss1 => ws1.flatMap(w => _amb(w :: ws, wss1)).headOption
+    }
+    _amb(Nil, wss.reverse)
+  }
+
+  def main(args: Array[String]) {
+    println(amb(List(List("the", "that", "a"),
+                     List("frog", "elephant", "thing"),
+                     List("walked", "treaded", "grows"),
+                     List("slowly", "quickly"))))
+  }
+}