题目：
Implement the following operations of a stack using queues.
Notes:
push to back, peek/pop from front, size, and is empty operations are valid.
题意及分析：用标准的queue实现stack。这里关键就是添加完成时，刚添加的点要在queue最前面，将queue的前面的点依次取出并添加到queue尾就可以实现这个stack添加功能。
代码：
public class MyStack {
Queue<Integer> queue ;
/** Initialize your data structure here. */
public MyStack() {
queue = new LinkedList<Integer>();
}
/** Push element x onto stack. */
public void push(int x) {
queue.add(x);
for(int i=0;i<queue.size()-1;i++){
queue.add(queue.poll());
}
}
/** Removes the element on top of the stack and returns that element. */
public int pop() {
return queue.poll();
}
/** Get the top element. */
public int top() {
return queue.peek();
}
/** Returns whether the stack is empty. */
public boolean empty() {
return queue.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();
*/
[LeetCode] 225. Implement Stack using Queues Java
原文：http://www.cnblogs.com/271934Liao/p/7029195.html