134_leetcode_LRU Cache

LRU缓存机制实现

最新推荐文章于 2025-09-13 14:08:34 发布

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本文介绍了一种使用双向链表和哈希表实现的LRU(Least Recently Used)缓存机制。该机制支持get和set操作，通过双向链表维护元素的访问顺序，最新访问的元素放在链表头部，最久未访问的元素放在链表尾部。当缓存容量达到上限时，会移除最久未访问的元素。

Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and set.

get(key) - Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.

set(key, value) - Set or insert the value if the key is not already present. When the cache reached its capacity, it should invalidate the least recently used item before inserting a new item.

1:构建数据结构，包含头尾节点的双向链表和unorder_map<int, doubleLinkList> 结构；2:消除最近最少使用的节点，当访问一个节点的时候，把被访问的节点放置在头节点的后面；当删除节点的时候，删除尾节点的前一个节点，并相应的对map结构进行处理。3:注意特殊情况

class LRUCache{
public:
    LRUCache(int capacity)
    {
        size = capacity;
        myMap.clear();
        
        head = new doubleLinkList(-1, -1);
        tail = new doubleLinkList(-1, -1);
        head->next = tail;
        tail->pre = head;
        
    }
    
    int get(int key)
    {
        unordered_map<int, doubleLinkList*>::iterator itr = myMap.find(key);
        
        if(itr != myMap.end())
        {
            doubleLinkList *tmp = itr->second;
            
            tmp->next->pre = tmp->pre;
            tmp->pre->next = tmp->next;
            putNodeTohead(tmp);
            return tmp->value;
        }
        else
        {
            return -1;
        }
    }
    
    void set(int key, int value)
    {
        unordered_map<int, doubleLinkList* >::iterator itr = myMap.find(key);
        if(itr != myMap.end())
        {
            doubleLinkList* tmp = itr->second;
            tmp->value = value;
            tmp->next->pre = tmp->pre;
            tmp->pre->next = tmp->next;
            putNodeTohead(tmp);
            return;
        }
        else
        {
            if(size > 0)
            {
                doubleLinkList* tmp = new doubleLinkList(key, value);
                putNodeTohead(tmp);
                size--;
                myMap[key] = tmp;
                return;
            }
            else
            {
                if(head->next == tail)
                {
                    return;
                }
                else
                {
                    doubleLinkList* delNode = tail->pre;
                    unordered_map<int, doubleLinkList* >::iterator itr = myMap.find(delNode->key);
                    myMap.erase(itr);
                    delNode->next->pre = delNode->pre;
                    delNode->pre->next = delNode->next;
                    delete delNode;
                    
                    doubleLinkList* tmp = new doubleLinkList(key, value);
                    putNodeTohead(tmp);
                    myMap[key] = tmp;
                    return;
                }
            }
        }
    }
    
private:
    struct doubleLinkList
    {
        int key;
        int value;
        doubleLinkList *pre;
        doubleLinkList *next;
        doubleLinkList(int x, int y) : key(x), value(y), pre(NULL), next(NULL){}
    };
    
    doubleLinkList* head;
    doubleLinkList* tail;
    int size;
    
    unordered_map<int, doubleLinkList* > myMap;
    
    void putNodeTohead(doubleLinkList* tmpNode)
    {
        head->next->pre = tmpNode;
        tmpNode->pre = head;
        tmpNode->next = head->next;
        head->next = tmpNode;
    }
    
};