Shulou(Shulou.com)06/03 Report--

This article mainly explains "how to implement a queue with two stacks". The content in the article is simple and clear, and it is easy to learn and understand. let's go deep into the editor's train of thought. Let's study and learn how to use two stacks to achieve a queue.

Before we get started, let's review the common methods of stacks and queues.

Common methods of Stack include the following:

Push (): stack method to add elements to the top of the stack

Pop (): unstack method that removes and returns elements from the top of the stack

Peek (): queries the elements at the top of the stack and does not remove them.

Common methods of queuing (Queue) include the following:

Offer (): queue joining method, adding elements to the end of the queue

Poll (): dequeue method that removes and returns elements from the head of the line

Peek (): querying the line header element does not remove the element.

With this pre-knowledge, let's look at today's topic.

Topic description

Implement a queue with two stacks. The declaration of the queue is as follows. Please implement its two functions, appendTail and deleteHead, to insert an integer at the end of the queue and delete an integer at the head of the queue. If there are no elements in the queue, the deleteHead operation returns-1.

Example 1:

Input: ["CQueue", "appendTail", "deleteHead", "deleteHead"] [[], [3], [], []] output: [null,null,3,-1]

Example 2:

Input: ["CQueue", "deleteHead", "appendTail", "appendTail", "deleteHead", "deleteHead"] [[], [], [5], [2], []] output: [null,-1,null,null,5,2]

Tip:

one

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