数据结构-队列

队列

队列的节点从头部删除（出队），从尾部插入（入队）

为先进先出的数据结构

实现分2个文件： ListModule.py 和 QueueModule.py

测试为1个文件：testQueue.py

ListModule.py 

  1 # ListModule.py
# Classes List and Node definitions.

class Node:
   """Single node in a data structure"""

   def __init__( self, data ):
      """Node constructor"""
      
      self._data = data
      self._nextNode = None
    
   def __str__( self ):
      """Node data representation"""

      return str( self._data )      

class List:
   """Linked list"""

   def __init__( self ):
      """List constructor"""

      self._firstNode = None
      self._lastNode = None

   def __str__( self ):
      """List string representation"""

      if self.isEmpty():
         return "empty"

      currentNode = self._firstNode
      output = []

      while currentNode is not None:
         output.append( str( currentNode._data ) )
         currentNode = currentNode._nextNode

      return " ".join( output )      

   def insertAtFront( self, value ):
      """Insert node at front of list"""

      newNode = Node( value )

      if self.isEmpty():  # List is empty
         self._firstNode = self._lastNode = newNode
      else:   # List is not empty
         newNode._nextNode = self._firstNode
         self._firstNode = newNode
        
   def insertAtBack( self, value ):
      """Insert node at back of list"""

      newNode = Node( value )

      if self.isEmpty():  # List is empty
         self._firstNode = self._lastNode = newNode
      else:  # List is not empty
         self._lastNode._nextNode =  newNode
         self._lastNode = newNode

   def removeFromFront( self ):
      """Delete node from front of list"""

      if self.isEmpty():  # raise exception on empty list
         raise IndexError, "remove from empty list"

      tempNode = self._firstNode

      if self._firstNode is self._lastNode:  # one node in list
         self._firstNode = self._lastNode = None
      else:
         self._firstNode = self._firstNode._nextNode

      return tempNode

   def removeFromBack( self ):
      """Delete node from back of list"""

      if self.isEmpty():  # raise exception on empty list
         raise IndexError, "remove from empty list"
     
      tempNode = self._lastNode

      if self._firstNode is self._lastNode:  # one node in list
         self._firstNode = self._lastNode = None
      else:
         currentNode = self._firstNode

         # locate second-to-last node
         while currentNode._nextNode is not self._lastNode:
               currentNode = currentNode._nextNode
               
         currentNode._nextNode = None
         self._lastNode = currentNode

      return tempNode
    
   def isEmpty( self ):
      """Returns true if List is empty"""

      return self._firstNode is None

QueueModule.py

# QueueModule.py
# Class Queue definition

from ListModule import List

class Queue( List ):
    """
    Queue composed from linked list
    """

    def __init__( self ):
        """
        Queue constructor
        """
        # List object data member
        self._queueList = List()

    def __str__( self ):
        """
        Queue string representation
        """
        # call List method __str__
        return str( self._queueList )

    def enqueue(self,element):
        """
        Enqueue element
        """
        # Method enqueue calls List method insertAtBack
        self._queueList.insertAtBack( element )

    def dequeue(self):
        """
        Dequeue element
        """
        # Method dequeue calls List method removeFromFront
        return self._queueList.removeFromFront()

    def isEmpty( self ):
        """
        Return 1 if Queue is empty
        """
        # call List method isEmpty
        return self._queueList.isEmpty()

testQueue.py

# testQueue.py
# Driver to test Class Queue

from QueueModule import Queue

queue = Queue()

print "Processing a queue"

for i in range( 4 ):
    # Insert items in Queue object by calling method enqueue
    queue.enqueue(i)
    print "The queue is:",queue

while not queue.isEmpty():
    # Remove items from Queue object by calling method dequeue
    dequeue = queue.dequeue()
    print dequeue,"dequeued"
    print "The queue is",queue