#Leet Code# LRU Cache

 1 struct Node {
 2     int key;
 3     int value;
 4     Node* next;
 5 };
 6 
 7 class LRUCache {
 8 public:
 9     LRUCache(int capacity) {
10         this->capacity = capacity;
11         this->curLength = 0;
12 
13         this->headNode = new Node();
14         this->headNode->key = -1;
15         this->headNode->value = -1;
16         this->headNode->next = NULL;
17 
18         this->lastNode = this->headNode;
19     }
20 
21     int get(int key) {
22         if (this->curLength == 0)
23             return -1;
24 
25         Node* tmpNode = reSequencing(key, -1);  
26         if (tmpNode != NULL) {
27             return tmpNode->value;
28         } else {
29             return -1;
30         }
31     }
32 
33     void set(int key, int value) {
34         if (this->capacity == 0) return;
35 
36         Node* tmpNode = reSequencing(key, value);  
37         if (tmpNode != NULL) {
38             tmpNode->value = value;
39             return;
40         } 
41 
42         if (this->curLength + 1 > this->capacity) {
43             if (this->headNode->next == this->lastNode) {
44                 delete this->lastNode;
45                 this->lastNode = this->headNode;
46             } else {
47                 Node* t = this->headNode->next->next;
48                 delete this->headNode->next;
49                 this->headNode->next = t;
50             }
51         }
52 
53         Node* newNode = new Node();
54         newNode->key = key;
55         newNode->value = value;
56         newNode->next = NULL;
57 
58         this->lastNode->next = newNode;
59         this->lastNode = newNode;
60 
61         curLength += 1;
62     }
63 
64     Node* reSequencing(int key, int value) {
65         Node* tmpNode = this->headNode;
66         Node* preNode;
67 
68         while (tmpNode != NULL) {
69             if (tmpNode->key == key) {
70                 break;
71             }
72 
73             preNode = tmpNode;
74             tmpNode = tmpNode->next;
75         }
76 
77         if (tmpNode != NULL && this->lastNode->key != key) {
78             preNode->next = tmpNode->next;
79 
80             this->lastNode->next = tmpNode;
81             this->lastNode = tmpNode;
82             tmpNode->next = NULL;
83         } 
84 
85         return tmpNode;
86     }
87 
88 private:
89     int capacity;
90     int curLength;
91 
92     Node* headNode;
93     Node* lastNode;
94 };