225. Implement Stack using Queues

Implement the following operations of a stack using queues.

• push(x) – Push element x onto stack.
• pop() – Removes the element on top of the stack.
• top() – Get the top element.
• empty() – Return whether the stack is empty.

Notes:

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

Update (2015-06-11):

The class name of the Java function had been updated to MyStack instead of Stack.

译：使用队列来实现以下栈的操作：

• push(x) – Push element x onto stack.
• pop() – Removes the element on top of the stack.
• top() – Get the top element.
• empty() – Return whether the stack is empty.

问题分析

关于栈和队列的相互实现，主要考察的是两者的概念和原理的清晰度，并且在队列实现中，需要了解相关语言的知识点，例如Java中实现队列结构的类有LinkedList，那么LinkedList中的哪些方法符合条件，就可以去看看Java源码。这里给出LeetCode中对这次的总结，各类操作的时间复杂度都分析明确，值得仔细看看：implement-stack-using-queues