[leetcode]Implement Stack using Queues

题目如下：

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).

就是对java中queue的复习，附上代码：

class MyStack {

private Queue<Integer> myqueue;

MyStack(){
myqueue = new LinkedList<Integer>();
}

// Push element x onto stack.
public void push(int x) {
Queue tmp = new LinkedList<Integer>();
tmp.add(x);
while(myqueue.size() != 0){
int data = myqueue.poll();
tmp.add(data);
}
myqueue = tmp;
}

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

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

// Return whether the stack is empty.
public boolean empty() {
return myqueue.size() == 0;
}
}

题目链接：`https://leetcode.com/problems/implement-stack-using-queues/