LeetCode232. Implement Queue using Stacks

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本文介绍了一种使用栈来实现队列数据结构的方法。通过两个栈的配合，实现了队列的基本操作，包括push、pop、peek和empty。文章提供了一个Python实现的例子，展示了如何使用列表来模拟栈，并通过具体的例子说明了其工作原理。

Implement the following operations of a queue using stacks.

push(x) -- Push element x to the back of queue.
pop() -- Removes the element from in front of queue.
peek() -- Get the front element.
empty() -- Return whether the queue is empty.

Example:

MyQueue queue = new MyQueue();

queue.push(1);
queue.push(2);  
queue.peek();  // returns 1
queue.pop();   // returns 1
queue.empty(); // returns false

Notes:

You must use only standard operations of a stack -- which means only push to top, peek/pop from top, size, and is empty operations are valid.
Depending on your language, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack.
You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).

思路：用python写的，也没有自带栈，用list模拟，很简单。

class MyQueue:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.s = []

    def push(self, x):
        """
        Push element x to the back of queue.
        :type x: int
        :rtype: void
        """
        self.s.append(x)

    def pop(self):
        """
        Removes the element from in front of queue and returns that element.
        :rtype: int
        """
        
        if len(self.s) == 0:
            return None
        else:     
            return self.s.pop(0)

            
    def peek(self):
        """
        Get the front element.
        :rtype: int
        """
        return self.s[0]

    def empty(self):
        """
        Returns whether the queue is empty.
        :rtype: bool
        """
        return not self.s