146. LRU Cache

Posted 2021-03-25 zhuangbijingdeboke

 1 class LRUCache {
 2 private:
 3     struct ListNode{
 4         int key,val;
 5         ListNode *pre;
 6         ListNode *next;
 7         ListNode(int x, int y) : key(x), val(y), pre(NULL), next(NULL){}
 8     };
 9     ListNode *head, *tail;
10     unordered_map<int, ListNode*> i2lmap;
11     int cap;
12     
13     void remove(ListNode* node){
14         if(node==head)
15             head = head->next;
16         if(node==tail)
17             tail = tail->pre;
18         if(node->pre)
19             node->pre->next=node->next;
20         if(node->next)
21             node->next->pre=node->pre;
22         i2lmap.erase(node->key);
23         delete node;
24     }
25     
26     void insert(int key, int value){
27         ListNode *node = new ListNode(key, value);
28         if(!head){
29             head=tail=node;
30         }
31         else{
32             tail->next=node;
33             node->pre=tail;
34             tail=node;
35         }
36         i2lmap[key]=node;
37     }
38     
39 public:
40     LRUCache(int capacity) {
41         cap = capacity;
42         head=tail=NULL;
43     }
44     
45     int get(int key) {
46         if(i2lmap.find(key)==i2lmap.end())
47             return -1;
48         
49         int value = i2lmap[key]->val;
50         remove(i2lmap[key]);
51         insert(key, value);
52         return value;
53     }
54     
55     void put(int key, int value) {
56         if(i2lmap.find(key)!=i2lmap.end())
57             remove(i2lmap[key]);
58         else if(i2lmap.size() == cap)
59             remove(head);
60         insert(key, value);
61     }
62 };
63 
64 /**
65  * Your LRUCache object will be instantiated and called as such:
66  * LRUCache* obj = new LRUCache(capacity);
67  * int param_1 = obj->get(key);
68  * obj->put(key,value);
69  */

用一个哈希表和双向链表来实现。

哈希表记录节点是否存在，并计数

双向链表实现按优先级删除和添加。链表头为长时间未使用的低优先级，链表尾为最近使用的高优先级。