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).
Credits:
Special thanks to @jianchao.li.fighter for adding this problem and all test cases.

import java.util.LinkedList;import java.util.Queue;public class MyStack {    private Queue<Integer> q1=new LinkedList<Integer>();    private Queue<Integer> q2=new LinkedList<Integer>();    /** Push element x onto stack. */    public void push(int x) {        if(!q1.isEmpty())            q1.add(x);        else            q2.add(x);    }    /** Removes the element on top of the stack and returns that element. */    public int pop() {        if(q1.isEmpty()){            int size=q2.size();            for(int i=1;i<size;i++){                q1.add(q2.poll());            }            return q2.poll();        }else{            int size=q1.size();            for(int i=1;i<size;i++){                q2.add(q1.poll());            }            return q1.poll();        }    }    /** Get the top element. */    public int top() {        int result;        if(q1.isEmpty()){            int size=q2.size();            for(int i=1;i<size;i++){                q1.add(q2.poll());            }            result=q2.poll();            q1.add(result);        }else{            int size=q1.size();            for(int i=1;i<size;i++){                q2.add(q1.poll());            }            result=q1.poll();            q2.add(result);        }        return result;    }    /** Returns whether the stack is empty. */    public boolean empty() {        return q1.isEmpty() && q2.isEmpty();    }}/** * Your MyStack object will be instantiated and called as such: * MyStack obj = new MyStack(); * obj.push(x); * int param_2 = obj.pop(); * int param_3 = obj.top(); * boolean param_4 = obj.empty(); */