public class Queue{ private Stack in; private Stack out; public Queue () { in = new Stack (); out = new Stack (); } public void add(E ele) { in.push(ele); } public E poll() { if (out.isEmpty()) { while (!in.isEmpty()) out.push(in.pop()); } if (out.isEmpty()) throw new NullPointerException("No element left!"); return out.pop(); } public static void main(String[] args) { Queue q = new Queue (); q.add(1); q.add(2); q.add(3); System.out.println(q.poll()); q.add(4); System.out.println(q.poll()); System.out.println(q.poll()); q.add(5); System.out.println(q.poll()); q.add(6); System.out.println(q.poll()); System.out.println(q.poll()); //System.out.println(q.poll()); } }
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Sunday, February 8, 2015
Implement queue with stack
This is a brilliant question with a brilliant answer: use two stacks!
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