题目链接：https://leetcode.cn/problems/implement-stack-using-queues/

1.用两个队列实现栈

C++代码如下：

class MyStack {
public:
    queue<int> dataQue; // 数据队列，该队列存储元素的顺序就是对应的栈存储元素的顺序
    queue<int> tempQue; // 临时队列，利用该队列实现dataQue中元素与新元素的次序调换

    MyStack() {

    }
    
    void push(int x) {
        tempQue.push(x);
        while (!dataQue.empty()) {
            tempQue.push(dataQue.front());
            dataQue.pop();
        }
        swap(dataQue, tempQue);
    }
    
    int pop() {
        int res = dataQue.front();
        dataQue.pop();
        return res;
    }
    
    int top() {
        return dataQue.front();
    }
    
    bool empty() {
        return dataQue.empty();
    }
};

/**
 * 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();
 */

2.用一个队列实现栈

class MyStack {
public:
    queue<int> dataQue; // 数据队列，该队列存储元素的顺序就是对应的栈存储元素的顺序

    MyStack() {

    }
    
    void push(int x) {
        int n = dataQue.size();
        dataQue.push(x);
        while (n--) {
            dataQue.push(dataQue.front());
            dataQue.pop();
        }
    }
    
    int pop() {
        int res = dataQue.front();
        dataQue.pop();
        return res;
    }
    
    int top() {
        return dataQue.front();
    }
    
    bool empty() {
        return dataQue.empty();
    }
};

/**
 * 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();
 */