Python学习笔记（四）——队列
1.基于列表：
class Queue:
def __init__(self):
self._qList = list()
def isEmpty(self):
return len(self) == 0
def __len__(self):
return len(self._qList)
def enqueue(self, item):
self._qList.append(item)
def dequeue(self):
assert not self.isEmpty(), "Cannot dequeue from an empty queue."
return self._qList.pop(0)2.基于循环数组：
# Implementation of the Queue ADT using a circular array.
import Array
class Queue:
def __init__(self, maxSize):
self._count = 0
self._front = 0
self._back = maxSize - 1
self._qArray = Array (maxSize)
def isEmpty(self):
return self._count == 0
def isFull(self):
return self._count == len(self._qArray)
def __len__(self):
return self._count
# Adds the given item to the queue.
def enquene(self, item):
assert not self.isFull(), "Cannot enqueue to a full queue."
maxSize = len(self._qArray)
self._back = (self._back + 1) % maxSize
self._qArray[self._back] = item
self._count += 1
# Removes and returns the first item in the queue.
def dequene(self):
assert not self.isEmpty(), "Cannot dequeue from an empty queue"
item = self._qArray[self._front]
maxSize = len(self._qArray)
self._front = (self._front + 1) % maxSize
self._count -= 1
return item3.基于链表：
class Queue:
def __init__(self):
self._qhead = None
self._qtail = None
self._count = 0
def isEmpty(self):
return self._qhead is None
def __len__(self):
return self._count
def enqueue(self, item):
node = _QueueNode(item)
if self.isEmpty():
self._qhead = node
else:
self._qtail.next = node
self._qtail = node
self._count += 1
def dequene(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
class _QueueNode(object):
def __init__(self, item):
self.item = item
self.next = None四、Priority Queue
1.unbound priority queue
# Implementation of the unbounded Priority Queue ADT using a Python list
# with new items appended to the end.
class PriorityQueue:
def __init__(self):
self._qList = list()
def isEmpty(self):
return len(self) == 0
def __len__(self):
return len(self._qList)
def enqueue(self, item, priority):
entry = _PriorityQEntry(item, priority)
self._qList.append(entry)
def dequene(self):
assert not self.isEmpty(), 'Cannot dequeue from an empty queue.'
highest = self._qList[0].priority
entry = self._qList[0]
for i in range(self.__len__()):
if self._qList[i].priority < highest:
highest = self._qList[i].priority
entry = self._qList[i]
index = self._qList.index(entry)
self._qList.pop(index)
return entry.item
class _PriorityQEntry(object):
def __init__(self, item, priority):
self.item = item
self.priority = priority
queue = PriorityQueue()
queue.enqueue(1,2)
queue.enqueue(2,7)
queue.enqueue(3,8)
queue.enqueue(4,0)
queue.enqueue(5,9)
queue.enqueue(6,1)
for i in range(6):
print(queue.dequene())
'''
output:
4
6
1
2
3
5
'''
2.bounded queue
from array import Array
from llistqueue import Queue
class BPriorityQueue:
def __init__(self, numLevels):
self.numLevels = numLevels
self._qSize = 0
self._qLevels = Array(numLevels)
for i in range(numLevels):
self._qLevels[i] = Queue()
def isEmpty(self):
return len(self) == 0
def __len__(self):
return self._qSize
def enqueue(self, item, priority):
assert priority >= 0 and priority < self.numLevels,\
"Invalid priority level."
self._qLevels[priority].enqueue(item)
self._qSize += 1
def dequeue(self):
assert not self.isEmpty(), "Cannot dequeue from an empty queue."
i = 0
p = len(self._qLevels)
while i < p and self._qLevels[i].isEmpty():
i += 1
return self._qLevels[i].dequene()
b = BPriorityQueue(5)
b.enqueue(1,4)
b.enqueue(2,3)
b.enqueue(3,2)
b.enqueue(4,0)
b.enqueue(5,1)
for i in range(5):
print(b.dequeue())
'''
output:
4
5
3
2
1
'''五、模拟飞机检票
未解决