[雪峰磁针石博客]Python经典面试题: 用3种方法实现堆栈和队列并示例实际应用场景
介绍
数据结构在计算机中组织存储，以便我们可以有效地访问和更改数据。 堆栈和队列是计算机科学中定义的最早的数据结构。
堆栈
遵循后进先出 (Last-in-First-Out LIFO)原则。
- push - 在堆栈顶部添加元素：
- pop - 删除堆栈顶部的元素：
队列
遵循先入先出(FIFO:First-in-First-Out)原则。
- enqueue - 在队列的开头添加元素：
- dequeue - 删除队列开头的元素：
使用列表实现堆栈和队列
Python的内置List数据结构k堆栈和队列操作的方法。
堆栈
letters = []
# Let's push some letters into our list
letters.append('c')
letters.append('a')
letters.append('t')
letters.append('g')
# Now let's pop letters, we should get 'g'
last_item = letters.pop()
print(last_item)
# If we pop again we'll get 't'
last_item = letters.pop()
print(last_item)
# 'c' and 'a' remain
print(letters) # ['c', 'a'] 执行结果
g
t
['c', 'a']队列
fruits = []
# Let's enqueue some fruits into our list
fruits.append('banana')
fruits.append('grapes')
fruits.append('mango')
fruits.append('orange')
# Now let's dequeue our fruits, we should get 'banana'
first_item = fruits.pop(0)
print(first_item)
# If we dequeue again we'll get 'grapes'
first_item = fruits.pop(0)
print(first_item)
# 'mango' and 'orange' remain
print(fruits) # ['c', 'a'] 执行结果
banana
grapes
['mango', 'orange']使用Deque库的堆栈和队列
deque是Double Ended Queue的缩写 - 可以获取存储的第一个或最后一个元素的通用队列，下面我们使用Deque库的堆栈和队列：
from collections import deque
# you can initialize a deque with a list
numbers = deque()
# Use append like before to add elements
numbers.append(99)
numbers.append(15)
numbers.append(82)
numbers.append(50)
numbers.append(47)
# You can pop like a stack
last_item = numbers.pop()
print(last_item) # 47
print(numbers) # deque([99, 15, 82, 50])
# You can dequeue like a queue
first_item = numbers.popleft()
print(first_item) # 99
print(numbers) # deque([15, 82, 50]) 执行结果
47
deque([99, 15, 82, 50])
99
deque([15, 82, 50])参考资料
更严格的实现
创建撤消功能 - 允许用户回溯他们的操作，直到会话开始。堆栈是这种情况的理想选择。 我们可以通过将其推送到堆栈来记录用户所采取的每个操作。 当用户想要撤消操作时，他们将从堆栈中弹出它。
游戏中，每次按下按钮，都会触发输入事件。 测试人员注意到，如果按钮按下得太快，游戏只处理第一个按钮，特殊动作将无效！可以使用队列修复它。 我们可以将所有输入事件排入队列。
#!/usr/bin/python3
# -*- coding: utf-8 -*-
# 项目实战讨论QQ群630011153 144081101
# python测试开发库汇总: https://github.com/china-testing/python-api-tesing/
# 本文最佳板式地址： https://www.jianshu.com/p/c990427ca608
# A simple class stack that only allows pop and push operations
class Stack:
def __init__(self):
self.stack = []
def pop(self):
if len(self.stack) < 1:
return None
return self.stack.pop()
def push(self, item):
self.stack.append(item)
def size(self):
return len(self.stack)
# And a queue that only has enqueue and dequeue operations
class Queue:
def __init__(self):
self.queue = []
def enqueue(self, item):
self.queue.append(item)
def dequeue(self):
if len(self.queue) < 1:
return None
return self.queue.pop(0)
def size(self):
return len(self.queue)
document_actions = Stack()
# The first enters the title of the document
document_actions.push('action: enter; text_id: 1; text: This is my favourite document')
# Next they center the text
document_actions.push('action: format; text_id: 1; alignment: center')
# As with most writers, the user is unhappy with the first draft and undoes the center alignment
document_actions.pop()
# The title is better on the left with bold font
document_actions.push('action: format; text_id: 1; style: bold')
input_queue = Queue()
# The player wants to get the upper hand so pressing the right combination of buttons quickly
input_queue.enqueue('DOWN')
input_queue.enqueue('RIGHT')
input_queue.enqueue('B')
# Now we can process each item in the queue by dequeueing them
key_pressed = input_queue.dequeue() # 'DOWN'
# We'll probably change our player position
key_pressed = input_queue.dequeue() # 'RIGHT'
# We'll change the player's position again and keep track of a potential special move to perform
key_pressed = input_queue.dequeue() # 'B'
# This can do the act, but the game's logic will know to do the special move
