leetcode 225: Implementing stacks with queues

Topic: Implementing stacks with queues

• Topic description:
  Use the queue to implement the following operations on the stack:
  push(x) – element x is pushed onto the stack
  pop() – remove the top element of the stack
  top() – get the top element of the stack
  empty() – return whether the stack is empty

Notice:

• You can only use the basic operations of the queue - namely push to back, peek/pop from front, size, and is empty which are legal.
• The language you are using may not support queues. You can use list or deque (double-ended queue) to simulate a queue, as long as it's standard queue operations.
• All operations are assumed to be valid (eg, no pop or top operations are called on an empty stack).

C++:
#include <queue>
class MyStack {
public:
    /** Initialize your data structure here. */
    MyStack() {

    }

    /** Push element x onto stack. */
    void push(int x) {
        std::queue<int> temp_queue;  //临时队列
        temp_queue.push(x);   //将新元素push进入临时队列temp_queue
        while(!_data.empty())    
        {
            temp_queue.push(_data.front());    //将原队列内容push进入临时队列temp_queue
            _data.pop();
        }
        while(!temp_queue.empty())
        {
            _data.push(temp_queue.front());   //将临时队列temp_queue元素push进入数据队列data_queue
            temp_queue.pop();
        }
    }

    /** Removes the element on top of the stack and returns that element. */
    int pop() {     //pop弹出栈顶并返回栈顶元素
        int x = _data.front(); //取栈顶元素，即为队列头部元素
        _data.pop();  //弹出队列头部元素
        return x;  //返回取出的队列头部元素x，即为栈顶元素
    }

    /** Get the top element. */
    int top() {
        return _data.front();  //返回栈顶即直接返回队列头部元素
    }

    /** Returns whether the stack is empty. */
    bool empty() {
        return _data.empty();   //
    }
private:
    std::queue<int> _data;   //_data数据队列存储元素的顺序就是栈存储元素的顺序
};

/**
 * 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();
 */