package com.sprint.datastructure;
import java.util.Stack;
import java.util.NoSuchElementException;
/**
* 用两个栈来实现一个队列
*
* @param <E>
*/
public class QueueWithTwoStacks<E> {
private Stack<E> stack1;
private Stack<E> stack2;
public QueueWithTwoStacks() {
stack1 = new Stack<E>();
stack2 = new Stack<E>();
}
public boolean isEmpty() {
return stack1.isEmpty() && stack2.isEmpty();
}
public int size() {
return stack1.size() + stack2.size();
}
public void enQueue(E item) {
if (item == null)
return;
stack1.push(item);
}
public E deQueue() {
if (isEmpty()) {
throw new NoSuchElementException("Queue is empty");
}
if (stack2.isEmpty()) {
moveStack1ToStack2();
}
return stack2.pop();
}
private void moveStack1ToStack2() {
while (!stack1.isEmpty()) {
stack2.push(stack1.pop());
}
}
}