> For the complete documentation index, see [llms.txt](https://r24zeng.gitbook.io/leetcode-notebook/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://r24zeng.gitbook.io/leetcode-notebook/bu-chong-6180-dao/225.-implement-stack-using-queues.md).

# 225. Implement Stack using Queues

\# Easy

{% hint style="info" %}
Three methods:

1. straight froward method:  use **queue 1** as main storage and **queue 2** as helper. Use **q2** when do `pop()`.
2. smart method: use two queues, **q1** stores all elements except top element, **q2** only stores top element.
3. one queue method: only complicated when doing `push()`, change the order to the **stack** order.

reference: <https://www.cnblogs.com/grandyang/p/4568796.html>
{% endhint %}

{% tabs %}
{% tab title="C++方法一" %}

```cpp
class MyStack {
public:
    /** Initialize your data structure here. */
    MyStack() {
        
    }
    
    /** Push element x onto stack. */
    void push(int x) {
        q1.push(x);
    }
    
    /** Removes the element on top of the stack and returns that element. */
    int pop() {
        while(q1.size() != 1) {
            int tmp = q1.front();
            q1.pop();
            q2.push(tmp);
        }
        int res = q1.front();
        q1.pop();
        while(q2.size() != 0) {
            int tmp = q2.front();
            q2.pop();
            q1.push(tmp);
        }
        return res;
    }
    
    /** Get the top element. */
    int top() {
        int res = pop();
        q1.push(res);
        return res;
    }
    
    /** Returns whether the stack is empty. */
    bool empty() {
        return q1.empty();
    }
    
private:
    queue<int> q1, q2;
};

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

{% endtab %}
{% endtabs %}