leetcode Implement Stack using Queues

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Implement Stack using Queues 题目：https://leetcode.com/problems/implement-stack-using-queues/

Implement Stack using Queues 

解题思路：使用两个队列实现栈，始终保持一个队列为空。

class MyStack {Queue<Integer> queue1=new LinkedList<>();Queue<Integer> queue2=new LinkedList<>();/** Initialize your data structure here. */public MyStack() {}/** Push element x onto stack. */public void push(int x) {if(queue1.isEmpty()){queue1.offer(x);while(!queue2.isEmpty()){Integer peek = queue2.peek();queue2.poll();queue1.offer(peek);}}else{queue2.offer(x);while(!queue1.isEmpty()){Integer peek = queue1.peek();queue1.poll();queue2.offer(peek);}}}/** Removes the element on top of the stack and returns that element. */public int pop() {if(!queue1.isEmpty()){return queue1.poll();}if(!queue2.isEmpty()){return queue2.poll();}return 0;}/** Get the top element. */public int top() {if(!queue1.isEmpty()){return queue1.peek();}if(!queue2.isEmpty()){return queue2.peek();}return 0;}/** Returns whether the stack is empty. */public boolean empty() {return queue1.isEmpty() && queue2.isEmpty();}
}

 

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