1 /*雙向鏈表特點：
  2  *1.每個節點含有兩個引用，previos和next,支持向前或向後的遍歷(除頭節點)
  3  *2.缺點插入或刪除的時候涉及到引用修改的比較多
  4  *註意：下面的雙向鏈表其實也實現了雙端鏈表
  5  *註意：在Java中多個引用可以指向同一個對象，也可以隨時改變引用的指向
  6  *      關於修改引用細心一點就可以 引用A = 引用B 表示A引用指向B引用指向的對象
  7  *應用:利用雙向鏈表可以實現雙端隊列
  8  * */
  9 
 10 public class MyDoubleLink {
 11     private Link first;
 
 12     private Link last;
 13     
 14     public boolean isEmpty(){
 15         return first == null;
 16     }
 17     
 18     public void insertFirst(int key){
 19         Link newLink = new Link(key);
 20         if(first == null){
 21             last = newLink;
 22         }
 23         else{
 
 24             first.previous = newLink;
 25         }
 26         newLink.next = first;//鏈未斷可以指向同一個
 27         first = newLink;
 28     }
 29     
 30     public void insertLast(int key){
 31         Link newLink = new Link(key);
 32         if(first == null){
 33             first = newLink;
 34         }
 
 35         else{
 36             last.next = newLink;
 37             newLink.previous = last;
 38         }
 39         last = newLink;
 40     }
 41     
 42     //插入指定值的後邊---其實是一種尾巴插入--此時鏈表非空才可以操作
 43     public boolean insertAfter(int key,int value){
 44         Link newLink = new Link(value);
 45         Link current = first;
 46         while(current.id != key){
 47             current = current.next;
 48             if(current == null){
 49                 return false;
 50             }
 51         }
 52         if(current == last){//find it at last item
 53             newLink.next = null;
 54             last = newLink;
 55         }
 56         else{
 57             newLink.next = current.next;
 58             current.next.previous = newLink;
 59         }
 60         newLink.previous = current;
 61         current.next = newLink;
 62         return true;
 63     }
 64     
 65     public Link deleteFirst(){
 66         Link temp = first;
 67         if(first.next == null){
 68             last = null;
 69         }
 70         else{
 71             first.next.previous = null;
 72         }
 73         first = first.next;
 74         return temp;
 75     }
 76     
 77     public Link deleteLast(){
 78         Link temp = last;
 79         if(first.next == null){
 80             first = null;
 81         }
 82         else{
 83             last.previous.next = null;
 84         }
 85         last = last.previous;
 86         return temp;
 87     }
 88     
 89     //按照值進行刪除--可能存在找不到的時候
 90     public Link delete(int key){
 91         Link current = first;
 92         while(current.id != key ){
 93             current = current.next;
 94             if(current == null){
 95                 return null;
 96             }
 97         }
 98         if(current == first){//find it at first item並非只有一個節點
 99             first = current.next;
100         }
101         else{  //find it not first item
102             current.previous.next = current.next;
103         }
104         
105         if(current == last){  //find it at last item
106             last = current.previous;
107         }
108         else{ //find it not last
109             current.next.previous = current.previous;
110         }
111         return current;
112     }
113     
114     public void diaplayFirstToLast(){
115         System.out.println("first to last");
116         Link current = first;
117         while(current != null){
118             System.out.print(current.id + " ");
119             current = current.next;
120         }
121         System.out.println();
122     }
123     
124     public void displayLastToFirst(){
125         System.out.println("last to first");
126         Link current = last;
127         while(current != null){
128             System.out.print(current.id + " ");
129             current = current.previous;
130         }
131         System.out.println();
132     }
133 }

雙向鏈表--Java實現