225. Implement Stack using Queues

mplement 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).

class Stack {
public:
    queue<int>queue1;
    queue<int>queue2;
    // Push element x onto stack.
    void push(int x) {
        if(queue1.empty())
        {
            queue1.push(x);
            while(!queue2.empty()){
                queue1.push(queue2.front());
                queue2.pop();
            }
        }
        else{
             queue2.push(x);
            while(!queue1.empty()){
                queue2.push(queue1.front());
                queue1.pop();
            }
        }
    }

    // Removes the element on top of the stack.
    void pop() {
        if(!queue1.empty())queue1.pop();
        if(!queue2.empty())queue2.pop();
    }

    // Get the top element.
    int top() {
        if(!queue1.empty())return queue1.front();
        if(!queue2.empty())return queue2.front();
    }

    // Return whether the stack is empty.
    bool empty() {
        return queue1.empty()&queue2.empty();
    }
};