1 改进链表
- head 添加和删除元素很容易;
- tail 只是添加元素容易;
- head 作为 队首
- 没有 虚拟头结点,注意链表为空的情况;
2 基于链表的队列
package linkedlist;
public interface Queue<E> {
int getSize();
boolean isEmpty();
void enqueue(E e);
E dequeue();
E getFront();
}
package linkedlist;
public class LinkedListQueue<E> implements Queue<E> {
private class Node {
public E e;
public Node next;
public Node(E e, Node next) {
this.e = e;
this.next = next;
}
public Node(E e) {
this(e, null);
}
public Node() {
this(null, null);
}
@Override
public String toString() {
return e.toString();
}
}
private Node head, tail;
private int size;
public LinkedListQueue() {
head = null;
tail = null;
size = 0;
}
@Override
public int getSize() {
return size;
}
@Override
public boolean isEmpty() {
return size == 0;
}
@Override
public void enqueue(E e) {
if (tail == null) {
tail = new Node(e);
head = tail;
} else {
tail.next = new Node(e);
tail = tail.next;
}
size++;
}
@Override
public E dequeue() {
if (isEmpty()) {
throw new IllegalArgumentException();
}
Node retNode = head;
head = head.next;
retNode.next = null;
if (head == null) {
tail = null;
}
size--;
return retNode.e;
}
@Override
public E getFront() {
if (isEmpty()) {
throw new IllegalArgumentException();
}
return head.e;
}
@Override
public String toString() {
StringBuilder res = new StringBuilder();
res.append("Queue:front ");
Node cur = head;
while (cur != null) {
res.append(cur + "->");
cur = cur.next;
}
res.append("Null tail");
return res.toString();
}
public static void main(String[] args) {
LinkedListQueue<Integer> queue = new LinkedListQueue<>();
for (int i = 0; i < 10; i++) {
queue.enqueue(i);
System.out.println(queue);
if (i % 3 == 2) {
queue.dequeue();
System.out.println(queue);
}
}
}
}
Queue:front 0->Null tail
Queue:front 0->1->Null tail
Queue:front 0->1->2->Null tail
Queue:front 1->2->Null tail
Queue:front 1->2->3->Null tail
Queue:front 1->2->3->4->Null tail
Queue:front 1->2->3->4->5->Null tail
Queue:front 2->3->4->5->Null tail
Queue:front 2->3->4->5->6->Null tail
Queue:front 2->3->4->5->6->7->Null tail
Queue:front 2->3->4->5->6->7->8->Null tail
Queue:front 3->4->5->6->7->8->Null tail
Queue:front 3->4->5->6->7->8->9->Null tail
Process finished with exit code 0