(java)Implement Stack using Queues_java implement stack using queues-优快云博客

本文链接：https://blog.youkuaiyun.com/martinmateng/article/details/50249563

本文介绍了一种利用两个队列实现栈数据结构的方法，并提供了详细的Java代码实现。该方法通过巧妙地调整元素进出队列的顺序，实现了栈的基本操作：push、pop、top和empty。

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Implement the following operations of a stack using queues.

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).
思路:用两个队列来实现栈的操作
1 对于push() 判断队列1是否为空，为空直接加进去，不为空，则将队列1中的元素依次出队，再依次入队列2，将新的元素插入队列1，然后再将队列2中的元素插入队列1
2对于pop() 由于1中的push操作已经把后进的元素放在队头，所以直接queue1.remove()即可。
3对于top()同理peek即可
4对于empty同理isempty即可
代码如下(已通过leetcode)
class MyStack {
// Push element x onto stack.
Queue<Integer> queue1= new LinkedList<Integer>();
Queue<Integer> queue2= new LinkedList<Integer>();
public void push(int x) {
if(queue1.isEmpty()) queue1.add(x);
else {
while(!queue1.isEmpty())
queue2.add(queue1.remove());
queue1.add(x);
while(!queue2.isEmpty())
queue1.add(queue2.remove());
}
}

// Removes the element on top of the stack.
public void pop() {
queue1.remove();
}

// Get the top element.
public int top() {
return queue1.peek();
}

// Return whether the stack is empty.
public boolean empty() {
return queue1.isEmpty();
}
}