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();
 */

public class MyStack {
   /** Initialize your data structure here. */
    Queue<Integer> q;
    
    public MyStack() {
        q = new LinkedList<>();
    }
    
    /** Push element x onto stack. */
    public void push(int x) {
        q.add(x);
    }
    
    /** Removes the element on top of the stack and returns that element. */
    public int pop() {
        int n = q.size();
        for(int i=0;i<n-1;i++){
            q.add(q.remove());
        }
        return q.remove();
    }
    
    /** Get the top element. */
    public int top() {
        int n = q.size();
        for(int i=0;i<n-1;i++){
            q.add(q.remove());
        }
        int ans = q.remove();
        q.add(ans);
        return ans;
    }
    
    /** Returns whether the stack is empty. */
    public boolean empty() {
        return q.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();
 */