用队列实现栈

class MyStack {
public:
    /** Initialize your data structure here. */
    MyStack() {
        
    }
    
    /** Push element x onto stack. */
    void push(int x) {
        queue<int> tmp_queue;//临时队列，用于辅助调换数据队列的元素顺序
        tmp_queue.push(x);
        while(data_queue.size())//假设data队列的数据：back 1 2 3 4 front,tmp队列是 5
        {
            tmp_queue.push(data_queue.front());//tmp队列就成了:back  4  5 front,data是：1 2 3
            data_queue.pop();
        }//tmp队列就成了:back  1 2 3 4  5 front
        while(tmp_queue.size())
        {
            data_queue.push(tmp_queue.front());
            tmp_queue.pop();
        }//data队列就成了:back  1 2 3 4  5 front, 5是最后进的，根据栈，5也该是先出的
    }
    
    /** Removes the element on top of the stack and returns that element. */
    int pop() {
        int x = data_queue.front();
        data_queue.pop();
        return x;
    }
    
    /** Get the top element. */
    int top() {
        return data_queue.front();
    }
    
    /** Returns whether the stack is empty. */
    bool empty() {
        return data_queue.empty();
    }
    
private:
    queue<int> data_queue;//实现栈的队列
};

/**
 * 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();
 */