Implement Queue using Stacks

class Queue {
public:
    // Push element x to the back of queue.
    void push(int x) {
        s1.push(x);
    }

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

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