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[Python数据结构] 使用 Circular List实现Queue
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[Python数据结构] 使用 Circular List实现Queue
1. Queue
队列，又称为伫列（queue），是先进先出（FIFO, First-In-First-Out）的线性表。在具体应用中通常用链表或者数组来实现。队列只允许在后端（称为rear）进行插入操作，在前端进行删除操作。队列的操作方式和堆栈类似，唯一的区别在于队列只允许新数据在后端进行添加。
Queue[维基百科]
2. Queue ADT
队列是一种抽象数据类型，其实例Q需要支持两种方法：
1）Q.enqueue(e) : Add an element to the back of queue.
2）Q.dequeue( ) : Remove and return the first element in the queue
另外，为了方便使用，我们还定义了以下方法：
3）Q.first() : Return the element at the front of the queue
4）Q.is_empty() : Return True if the queue is empty
5）len(Q) : Return the number of elements in the queue
3. Queue Implementation
class Empty(Exception):
"""Error attempting to access an element from an empty container"""
pass
class ArrayQueue():
"""FIFO queue implementation using a python list as underlying storage."""
Default_capacity = 10 def __init__(self):
"""Create an empty queue"""
self.data = [None] * ArrayQueue.Default_capacity # reference to a list instance with a fixed capacity.
self.size = 0 # an integer representing the current number of elements stored in the queue.
self.front = 0 # an integer that represents the index within data of the first element of the queue. def __len__(self):
"""Return the number od elements in the queue."""
return self.size def is_empty(self):
"""Return True if the queue is empty."""
return self.size == 0 def first(self):
"""Return the element at the front of the queue. Raise Empty exception if the queue is empty."""
if self.is_empty():
raise Empty('the queue is empty')
return self.data[self.front] def dequeue(self):
"""Remove and return the first element in the queue. Raise Empty exception if the queue is empty."""
if self.is_empty():
raise Empty('the queue is empty')
answer = self.data[self.front]
self.data[self.front] = None
self.front = (self.front + 1) % len(self.data)
self.size -= 1
return answer def enqueue(self, e):
"""Add an element to the back of queue."""
if self.size == len(self.data):
self.resize(2 * len(self.data))
avail = (self.front + self.size) % len(self.data)
self.data[avail] = e
self.size += 1 def resize(self, cap):
"""Resize to a new list of capacity."""
old = self.data
self.data = [None] * cap
walk = self.front
for k in range(self.size):
self.data[k] = old[walk]
walk = (1 + walk) % len(old)
self.front = 0
4. 执行结果：
q = ArrayQueue()
l = np.random.randint(0, 10, size=(20, ))
for i in l:
q.enqueue(i)
q.data
[0, 1, 5, 3, 9, 5, 0, 9, 1, 0, 4, 6, 7, 0, 2, 5, 9, 3, 3, 9]
q.dequeue()
0
q.data
[None, 1, 5, 3, 9, 5, 0, 9, 1, 0, 4, 6, 7, 0, 2, 5, 9, 3, 3, 9]
q.first()
1
q.data
[None, 1, 5, 3, 9, 5, 0, 9, 1, 0, 4, 6, 7, 0, 2, 5, 9, 3, 3, 9]
