# -*-coding: utf-8 -*-
# Author :writen by Qiusheng Li
# Time: 2014/08/19
# Email:[email protected]
# enqueue Insert an item at the back of the queue
# dequeue Remove an item from the front of the queue
# peek/front Retrieve an item at front of the queue without removing it
# empty/size Check whether the queue is empty or return its size
# using list impliment the Queue
#node another approach is to implement a queue as a container for nodes,as we have
#done for stacks,but now the nodes are inserted and removed in a FIFO order
class Node(object):
def __init__(self,value=None):
self.value = value
self.next =None
class Queue2(object):
'''container nodes to implement a queue class'''
def __init__(self):
self.first =None # point to the first node
self.pre = None # point to the last node
def enqueue(self,value):
node = Node(value)
if self.first == None:
self.first = node
else:
self.pre.next = node
self.pre = node
def dequeue(self):
if self.first:
value = self.first.value # get value object is better than get node object
self.first = self.first.next
return value
# else: # don't use else, if contains return
raise Exception('Queue is empty')
def peek(self):
if self.first:
return self.first.value
else:
return None
def isEmpty(self):
return bool(self.first)
def size(self):
if self.first == None:
return 0
node = self.first
i = 0
while node:
i += 1
node = node.next
return i
def Queue2Main():
queue = Queue2()
queue.enqueue(1)
queue.enqueue(2)
queue.enqueue(3)
print "size : ",queue.size()
print "peek: ",queue.peek()
print "dequeue: ",queue.dequeue()
print "size : ",queue.size()
print "peek: ",queue.peek()
print "dequeue: ",queue.dequeue()
print "dequeue: ",queue.dequeue()
print "size : ",queue.size()
print "peek: ",queue.peek()
'''testing result
size : 3
peek: 1
dequeue: 1
size : 2
peek: 2
dequeue: 2
dequeue: 3
size : 0
peek: None
'''
if __name__ == '__main__':
Queue2Main()
