queue implemented with link list

Author: lyuka

Diff for: llistqueue.py

@@ -0,0 +1,55 @@
+# Implementation of the Queue ADT using a linked list.
+class Queue:
+    # Creates an empty queue.
+    def __init__( self ):
+        self._qhead = None
+        self._qtail = None
+        self._count = 0
+
+    # Returns True if the queue is empty.
+    def isEmpty( self ):
+        return self._qhead is None
+
+    # Returns the number of items in the queue.
+    def __len__( self ):
+        return self._count
+
+    # Adds the given item to the queue.
+    def enqueue( self, item ):
+        node = _QueueNode( item )
+        if self.isEmpty():
+            self._qhead = node
+        else:
+            self._qtail.next = node
+        self._qtail = node
+        self._count += 1
+
+    # Removes and returns the first item in the queue.
+    def dequeue( self ):
+        assert not self.isEmpty(), "Cannot dequeue from an empty queue."
+        node = self._qhead
+        if self._qhead is self._qtail:
+            self._qtail = None
+        self._qhead = self._qhead.next
+        self._count -= 1
+        return node.item
+
+# Private storage class for creating the linked list ndoes.
+class _QueueNode( object ):
+    def __init__( self, item ):
+        self.item = item
+        self.next = None
+
+if __name__ == '__main__':
+    Q = Queue()
+    Q.enqueue( 28 )
+    #Q.enqueue( 19 )
+    #Q.enqueue( 45 )
+    #Q.enqueue( 13 )
+    #Q.enqueue( 7 )
+
+    for i in range( len(Q) ):
+        cur_item = Q.dequeue()
+        print cur_item,
+    print ''
+    print Q._qhead, Q._qtail