使用链表实现队列

使用链表实现队列

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  1 public class LinkedListQueue2<E> implements Queue<E> {
  2 
  3     private class Node {
  4         public E e;
  5         public Node next;
  6         
  7         public Node(E e, Node next) {
  8             this.e = e;
  9             this.next = next;
 10         }
 11         
 12         public Node(E e) {
 13             this(e, null);
 14         }
 15         
 16         public Node() {
 17             this(null, null);
 18         }
 19         
 20         @Override
 21         public String toString() {
 22             return e.toString();
 23         }
 24     }
 25 
 26     private Node dummyHead, tail;
 27     private int size;
 28     
 29     public LinkedListQueue2() {
 30         dummyHead = new Node();
 31         tail = dummyHead;
 32         size = 0;
 33     }
 34 
 35     @Override
 36     public int getSize() {
 37         return size;
 38     }
 39 
 40     @Override
 41     public boolean isEmpty() {
 42         return size == 0;
 43     }
 44 
 45     @Override
 46     public void enqueue(E e) {
 47 
 48         tail.next = new Node(e);
 49         tail = tail.next;
 50     
 51         size++;
 52     }
 53 
 54     @Override
 55     public E dequeue() {
 56         if(this.isEmpty()) {
 57             throw new IllegalArgumentException("Dequeue failed. Queue is empty.");
 58         }
 59         
 60         Node retNode = dummyHead.next;
 61         dummyHead.next = retNode.next;
 62         retNode.next = null;
 63         if(dummyHead.next == null) {
 64             tail = dummyHead;
 65         }
 66         size--;
 67         return retNode.e;
 68     }
 69 
 70     @Override
 71     public E getFront() {
 72         if(isEmpty()) {
 73             throw new IllegalArgumentException("Queue is empty.");
 74         }
 75         return dummyHead.next.e;
 76     }
 77 
 78     @Override
 79     public String toString() {
 80         StringBuilder res = new StringBuilder();
 81         res.append("Queue: front ");
 82         Node cur = dummyHead.next;
 83         while(cur != null) {
 84             res.append(cur + "->");
 85             cur = cur.next;
 86         }
 87         res.append("NULL tail");
 88         
 89         return res.toString();        
 90     }
 91     
 92     public static void main(String[] args) {
 93         LinkedListQueue2<Integer> queue = new LinkedListQueue2<>();
 94         for(int i=0; i<10; i++) {
 95             queue.enqueue(i);
 96             System.out.println(queue);
 97         
 98             if(i % 3 == 2) {
 99                 queue.dequeue();
100                 System.out.println(queue);
101             }
102         }
103         System.out.println(queue.getSize());
104         for(int i=0; i<7; i++) {
105             queue.dequeue();
106             System.out.println(queue);
107         }
108     }
109 }