leetcode Implement Stack using Queues

Implement the following operations of a stack using queues.

• push(x) -- Push element x onto stack.
• pop() -- Removes the element on top of the stack.
• top() -- Get the top element.
• empty() -- Return whether the stack is empty.

Notes:

• You must use only standard operations of a queue -- which means only push to back, peek/pop from front, size, and is empty operations are valid.
• Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.
• You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack)

很简单一道题，如果用栈实现队列有点难度，还需要两个栈。用队列实现栈的话还是比较简单的，用一个队列就可以完成了。

class Stack {
public:
    queue<int> Queue1;
    int* back,*tmp;
    // Push element x onto stack.
    void push(int x) {
        Queue1.push(x);
        
        
    }

    // Removes the element on top of the stack.
    void pop() {
        back=&Queue1.back();
        while(&Queue1.front()!=back){
            tmp=&Queue1.front();
            Queue1.pop();
            Queue1.push(*tmp);
        }
        Queue1.pop();
    }

    // Get the top element.
    int top() {
        return Queue1.back();
    }

    // Return whether the stack is empty.
    bool empty() {
        return Queue1.empty();
        
    }
};