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import java.util.LinkedList;

import java.util.Queue;

/**

* https://leetcode.com/articles/implement-stack-using-queues/

*/

public class MyStack {

private Queue<Integer> mQueue, mQueueTmp;

public MyStack() {

mQueue = new LinkedList<Integer>();

mQueueTmp = new LinkedList<Integer>();

}

// Push element x onto stack.

public void push(int x) {

mQueue.add(x);

}

// Removes the element on top of the stack.

public void pop() {

while (!mQueue.isEmpty()) {

int n = mQueue.poll();

if (!mQueue.isEmpty()) {

mQueueTmp.add(n);

}

}

swap();

}

private void swap() {

Queue<Integer> queue = mQueue;

mQueue = mQueueTmp;

mQueueTmp = queue;

}

// Get the top element.

public int top() {

int top = 0;

while (!mQueue.isEmpty()) {

top = mQueue.poll();

mQueueTmp.add(top);

}

swap();

return top;

}

// Return whether the stack is empty.

public boolean empty() {

return mQueue.isEmpty();

}

/** 这种做法只用一个Queue

private LinkedList<Integer> q1 = new LinkedList<>();

// Push element x onto stack.

public void push(int x) {

q1.add(x);

int sz = q1.size();

while (sz > 1) {

q1.add(q1.remove());

sz--;

}

}

// Removes the element on top of the stack.

public void pop() {

q1.remove();

}

// Get the top element.

public int top() {

return q1.peek();

}

// Return whether the stack is empty.

public boolean empty() {

return q1.isEmpty();

}*/

}