力扣146. LRU 缓存

 

① 刚开始的思路是哈希表+一个环形缓冲区，但是看到条件中可以重复，那这样可就麻烦了，另外，真的没有想到哈希表中存地址，另外list中既要保存key，也要保存value，按理说只有value就可以，但是要考虑一个点，就是size达到capacity的时候，要通过key才能找到删除哈希表中的哪一个；

② c++的链表要手搓。。。

③ 有一个优化点，就是反复利用已经存在的listnode，将要淘汰的node直接挪到前面，改变key，这样就不用重新申请内存和释放内存了

 

题目：【https://leetcode.cn/problems/lru-cache/?envType=study-plan-v2&envId=top-interview-150】

 

 1 class DListNode {
 2 public:
 3     int key;
 4     int value;
 5     DListNode* prev;
 6     DListNode* next;
 7     DListNode(int _key)
 8         : key(_key)
 9         , prev(NULL)
10         , next(NULL)
11     {}
12     DListNode(int _key, int _value)
13         : key(_key)
14         , value(_value)
15         , prev(NULL)
16         , next(NULL)
17     {}
18 };
19 
20 class LRUCache {
21 public:
22     LRUCache(int capacity)
23         : m_size(0)
24         , m_capacity(capacity)
25         , m_head(new DListNode(0))
26         , m_tail(new DListNode(0))
27     {
28         m_head->next = m_tail;
29         m_tail->prev = m_head;
30     }
31     
32     int get(int key) {
33         if (m_keys.count(key) <= 0)
34             return -1;
35 
36         DListNode* t = m_keys[key];
37         removeListNode(t->prev, t->next);
38         insertListNode(m_head, m_head->next, t);
39         return t->value;
40     }
41 
42     void put(int key, int value) {
43         DListNode* tn = m_keys[key];
44         if (NULL == tn) {
45             if (m_size >= m_capacity) {
46                 tn = m_tail->prev;
47                 m_keys.erase(tn->key);
48                 tn->key = key;
49                 removeListNode(tn->prev, tn->next);
50             } else {
51                 tn = new DListNode(key);
52                 m_size++;
53             }
54         } else {
55             if (m_head->next == tn) {
56                 tn->value = value;
57                 return ;
58             }
59             removeListNode(tn->prev, tn->next);
60         }
61 
62         insertListNode(m_head, m_head->next, tn);
63 
64         tn->value = value;
65 
66         m_keys[key] = tn;
67     }
68 
69 private:
70     void insertListNode(DListNode* prev, DListNode* next, DListNode* node)
71     {
72         node->next = next;
73         node->prev = prev;
74         prev->next = node;
75         next->prev = node;
76     }
77     void removeListNode(DListNode* prev, DListNode* next)
78     {
79         prev->next = next;
80         next->prev = prev;
81     }
82 
83 private:
84     unordered_map<int, DListNode*> m_keys;
85     int m_size;
86     int m_capacity;
87     DListNode* m_head;
88     DListNode* m_tail;
89 };
90 
91 /**
92  * Your LRUCache object will be instantiated and called as such:
93  * LRUCache* obj = new LRUCache(capacity);
94  * int param_1 = obj->get(key);
95  * obj->put(key,value);
96  */

 

posted @ 2025-05-08 11:15  J&YANG  阅读(14)  评论(0)    收藏  举报