package com.jamal;
/**
* @author xiaoxiang
* @title: DoubleEndsQueue
* @projectName queue
* @description: TODO
* @date 2019/8/2914:27
*/
public class DoubleEndsQueue {
private static class Node {
String item;
Node next;
Node prev;
Node(Node prev, String element, Node next) {
this.item = element;
this.next = next;
this.prev = prev;
}
}
transient Node first;
/**
* Pointer to last node.
* Invariant: (first == null && last == null) ||
* (last.next == null && last.item != null)
*/
transient Node last;
public void enqueueFirst(String e) {
final Node f = first;
final Node newNode = new Node(null, e, f);
first = newNode;
if (f == null)
last = newNode;
else
f.prev = newNode;
}
public void enqueueLast(String e) {
final Node l = last;
final Node newNode = new Node(l, e, null);
last = newNode;
if (l == null)
first = newNode;
else
l.next = newNode;
}
public String dequeueFirst() {
if (first == null) return null;
final Node f = first;
String element = f.item;
Node next = f.next;
f.item = null;
f.next = null; // help GC
first = next;
if (next == null)
last = null;
else
next.prev = null;
return element;
}
public String dequeueLast() {
final Node l = last;
if (last == null) return null;
String element = l.item;
Node prev = l.prev;
l.item = null;
l.prev = null;
last = prev;
if (prev == null)
first = null;
else
prev.next = null;
return element;
}
// 输出队列全部内容
public void displayAll() {
while (first !=null){
System.out.print(first.item+" ");
first = first.next;
}
System.out.println("===============");
}
}