> For the complete documentation index, see [llms.txt](https://dfine.gitbook.io/leetcode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://dfine.gitbook.io/leetcode/232.implement_queue_using_stack.md).

# 232.Implement Queue Using Stack

**232.Implement Queue Using Stacks**

难度:Easy

> 使用栈实现队列的下列操作：

push(x) -- 将一个元素放入队列的尾部。 pop() -- 从队列首部移除元素。 peek() -- 返回队列首部的元素。 empty() -- 返回队列是否为空。

```
示例:

MyQueue queue = new MyQueue();

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

说明:

你只能使用标准的栈操作 -- 也就是只有 push to top, peek/pop from top, size, 和 is empty 操作是合法的。 你所使用的语言也许不支持栈。你可以使用 list 或者 deque（双端队列）来模拟一个栈，只要是标准的栈操作即可。 假设所有操作都是有效的 （例如，一个空的队列不会调用 pop 或者 peek 操作）。

队列的特性是FIFO，栈的特性是LIFO，两个栈就可实现FIFO。

```
class MyQueue {
private:
        stack<int> mq1;
        stack<int> mq2;
public:
    /** Initialize your data structure here. */
    MyQueue() {

    }
    
    /** Push element x to the back of queue. */
    void push(int x) {
        if(mq2.empty())
            mq2.push(x);
        else
        {
            while(!mq2.empty())
            {
                mq1.push(mq2.top());
                mq2.pop();
            }
            mq2.push(x);
            while(!mq1.empty())
            {
                mq2.push(mq1.top());
                mq1.pop();
            }
        }
   
    }
    
    /** Removes the element from in front of queue and returns that element. */
    int pop() {
        int t=mq2.top();
        mq2.pop();
        return t;

        
    }
    
    /** Get the front element. */
    int peek() {
        return mq2.top();
    }
    
    /** Returns whether the queue is empty. */
    bool empty() {
        return mq2.empty();
    }
};

/**
 * Your MyQueue object will be instantiated and called as such:
 * MyQueue* obj = new MyQueue();
 * obj->push(x);
 * int param_2 = obj->pop();
 * int param_3 = obj->peek();
 * bool param_4 = obj->empty();
 */
```


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://dfine.gitbook.io/leetcode/232.implement_queue_using_stack.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.