python数据结构之队列

本篇我以队列的数据类型和操作方法两个方面总结学习笔记

队列(Queue)

• 一种先进先出（FIFO）的线性数据结构，插入操作在队尾（tail）进行，删除操作在队首（head）进行。
• 列可以通过（循环）数组或链表轻松实现

一、数据类型

• Queue() 创建队列
• enqueue(item) 向队尾插入项
• dequeue() 返回队首的项，并从队列中删除该项
• empty() 判断队列是否为空
• size() 返回队列中项的个数

操作示意图

注：front即head，rear即tail

二、代码实现

'''
使用Python的内建类型list列表实现很方便
'''
class Queue():
    def __init__(self):
        self.items = []
　　
    #增于尾后tail
    def enqueue(self, item):
        self.items.append(item)
    
    #删于头首head
    def dequeue(self):
        return self.items.pop(0)

    def empty(self):
        return self.size() == 0

    def size(self):
        return len(self.items)

'''
动态数组实现队列并不用内置方法
'''
class ArrayQueue:
    DEFAULT_CAPACITY = 10
    def __init__(self):
        self._data = [None] * ArrayQueue.DEFAULT_CAPACITY
        self._size = 0
        self._front = 0
        
    def __len__(self):
        return self._size
    
    def is_empty(self):
        return self._size == 0
    
    #O(1)
    def first(self):
        if self.is_empty( ):
            raise ValueError( 'Queue is empty' )
        return self._data[self._front]
    
    #O(1)
    def dequeue(self):
        if self.is_empty( ):
            raise ValueError( '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
    
    #O(1)
    def enqueue(self, e):
        if self._size == len(self._data):
            self._resize(2 * len(self._data)) #如果满了开拓两倍空间
        pos = (self._front + self._size) % len(self._data)
        self._data[pos] = e
        self._size += 1
        
    def resize(self, cap):
        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
        
    def printqueue(self):
        for i in range(self._size):
            pos = (self._front + self._size - 1 - i) % len(self._data)
            #print(str(i), ": ", str(pos))
            print(self._data[pos], end = " ")  
        print()

'''
链表
模块方法来自链表笔记代码
'''
from LinkedList import LinkedList
from LinkedList import Node

class LinkedQueue(object):
    def __init__(self):
        self.head = None
        self.tail = None
        self.count = 0  
    
    #O(1)
    def enqueue(self, value):
        new_node = Node(value)

        if self.tail is not None:
            self.tail.next = new_node

        else:
            self.head = new_node

        self.tail = new_node
        self.count += 1
    
    #O(1)
    def dequeue(self):
        if not self.is_empty():
            # print head to next node
            tmp = self.head
            self.head = self.head.next
            print("dequeue sucess")
            self.count -= 1
            return tmp
        else:
            raise ValueError("Empty QUEUE")

    def is_empty(self):
        if self.head is None and self.tail is None:
            return True
        else:
            return False

    def peek(self):
        return self.head.data

        
    def __len__(self):
        return self.count    

    def is_empty(self):
        return self.count == 0
    
    def print(self):
        node = self.head
        while node:
            print(node.value, end = " ")
            node = node.next
        print('')