tasks a-s

Task/Queue-Definition/Scala/queue-definition-1.scala

@@ -0,0 +1,34 @@
+class Queue[T] {
+  private[this] class Node[T](val value:T) {
+    var next:Option[Node[T]]=None
+    def append(n:Node[T])=next=Some(n)
+  }
+  private[this] var head:Option[Node[T]]=None
+  private[this] var tail:Option[Node[T]]=None
+
+  def isEmpty=head.isEmpty
+
+  def enqueue(item:T)={
+    val n=new Node(item)
+    if(isEmpty) head=Some(n) else tail.get.append(n)
+    tail=Some(n)
+  }
+	
+  def dequeue:T=head match {
+    case Some(item) => head=item.next; item.value
+    case None => throw new java.util.NoSuchElementException()
+  }
+
+  def front:T=head match {
+    case Some(item) => item.value
+    case None => throw new java.util.NoSuchElementException()
+  }
+
+  def iterator: Iterator[T]=new Iterator[T]{
+    private[this] var it=head;
+    override def hasNext=it.isDefined
+    override def next:T={val n=it.get; it=n.next; n.value}
+  }
+
+  override def toString()=iterator.mkString("Queue(", ", ", ")")
+}

Task/Queue-Definition/Scala/queue-definition-2.scala

@@ -0,0 +1,11 @@
+val q=new Queue[Int]()
+println("isEmpty = " + q.isEmpty)
+try{q dequeue} catch{case _:java.util.NoSuchElementException => println("dequeue(empty) failed.")}
+q enqueue 1
+q enqueue 2
+q enqueue 3
+println("queue   = " + q)
+println("front   = " + q.front)
+println("dequeue = " + q.dequeue)
+println("dequeue = " + q.dequeue)
+println("isEmpty = " + q.isEmpty)