1 package leetcode;
 2 
 3 import java.util.HashMap;
 4 import java.util.Map;
 5 
 6 class Node{
 7     int key;
 8     int value;
 9     Node pre;
10     Node next;
11     Node(int key,int value){
12         this.key=key;
13         this.value=value;
14         this.pre=null;
15         this.next=null;
16     }
17 }
18 class CacheList{
19     private Node head;
20     private Node tail;
21     CacheList(int capacity){
22         head = new Node(0,0);
23         tail = new Node(0,0);
24         head.next=tail;
25         tail.pre=head;
26     }
27     public void insertFirst(Node n){
28         n.next=head.next;
29         head.next.pre=n;
30         head.next=n;
31         n.pre=head;
32         
33     }
34     public Node removeLast(){
35         Node re = tail.pre;
36         tail.pre.pre.next=tail;
37         tail.pre=tail.pre.pre;
38         return re;
39     }
40     public void shiftToFirst(Node n){
41         n.pre.next=n.next;
42         n.next.pre=n.pre;
43         insertFirst(n);
44     }
45 }
46 
47 public class LRUCache {
48      Map<Integer,Node> map;
49      CacheList cacheList;
50      int capacity;
51     public LRUCache(int capacity) {
52         map = new HashMap<Integer,Node>();
53         cacheList= new CacheList(capacity);
54         this.capacity=capacity;
55     }
56     
57     public int get(int key) {
58         if(map.get(key)==null)
59         return -1;
60         else {
61             Node n= (Node) map.get(key);
62             cacheList.shiftToFirst(n);
63             return n.value;
64         }
65     }
66   
67     
68     public void set(int key, int value) {
69         if(map.containsKey(key)){
70              Node come= (Node) map.get(key);
71              come.value=value;
72              cacheList.shiftToFirst(come);;
73         }else{
74             if(map.size()==capacity){
75                 Node old=cacheList.removeLast();
76                 map.remove(old.key);
77                          
78             }
79             Node nn=new Node(key,value);
80             cacheList.insertFirst(nn);
81             map.put(key, nn);
82         }
83         
84 
85     }
86     public static void main(String[] args){
87         LRUCache l = new LRUCache(1);
88         l.set(2, 1);
89         System.out.println(l.get(2));
90         l.set(3, 2);
91         System.out.println(l.get(2));
92         System.out.println(l.get(3));
93 
94     }
95 }