leetcode-225-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).

用队列实现栈的操作。

class Stack {

public:
    queue<int> q1;
    queue<int> q2;
    int count = 0;
    // Push element x onto stack.
    void push(int x) {
        q1.push(x);
        count++;
    }

    // Removes the element on top of the stack.
    void pop() {
        while(count>1)
        {
            q2.push(q1.front());
            q1.pop();
            count--;
        }
        q1.pop();
        count--;
        while(!q2.empty())
        {
            q1.push(q2.front());
            count++;
            q2.pop();
        }
    }

    // Get the top element.
    int top() {
      return q1.back();

    }

    // Return whether the stack is empty.
    bool empty() {
        return q1.empty();
    }
};