Implement Queue using Stacks

class Queue {
public:
    // Push element x to the back of queue.
    void push(int x) {
        while (!s2.empty())
        {
            int val = s2.top();
            s1.push(val);
            s2.pop();
        }
        s1.push(x);
    }

    // Removes the element from in front of queue.
    void pop(void) {
        while (!s1.empty())
        {
            int val = s1.top();
            s2.push(val);
            s1.pop();
        }
        if (!s2.empty())
            s2.pop();
    }

    // Get the front element.
    int peek(void) {
        while (!s1.empty())
        {
            int val = s1.top();
            s2.push(val);
            s1.pop();
        }
        return s2.top();
    }

    // Return whether the queue is empty.
    bool empty(void) {
        if (s1.empty() && s2.empty())
            return true;
        else
            return false;
    }

private:
    stack<int> s1;
    stack<int> s2;
};