LRU

LRU(c++实现)

链接:https://leetcode-cn.com/problems/lru-cache/

struct DLinkedNode{
    int key,value;
    DLinkedNode* prev;
    DLinkedNode* next;
    DLinkedNode():key(0),value(0),prev(nullptr),next(nullptr){}
    DLinkedNode(int _key,int _value):key(_key),value(_value),prev(nullptr),next(nullptr){}
};
class LRUCache {
private:
    unordered_map<int,DLinkedNode*> cache;
    DLinkedNode* head;//表头
    DLinkedNode* tail;//表尾
    int size;//当前长度
    int capacity;//缓存长度限制
public:
    LRUCache(int _capacity) {
        size = 0;
        capacity = _capacity;
        head = new DLinkedNode();
        tail = new DLinkedNode();
        head->next = tail;
        tail->prev = tail; 
    }
    //查找有没有key
    int get(int key) {
        if(!cache.count(key)){
            return -1;
        }
        //如果 key 存在,先通过哈希表定位，再移到头部
        DLinkedNode* node = cache[key];
        moveToHead(node);
        return node->value;

    }

    void put(int key, int value) {
        if(!cache.count(key)){
            //如果 key 不存在的话，就建一个新节点
            DLinkedNode* node = new DLinkedNode(key,value);
            //加入hash表
            cache[key] = node;
            //添加到链表的头部
            addToHead(node);
            ++size;
            //如果超出容量
            if(size > capacity){
                //删除尾部节点
                DLinkedNode* removed = removeTail();
                //
                cache.erase(removed->key);
                delete removed;
                --size;
            }
        }
        else{
            //如果 key 存在，就通过hash表定位，然后更新value
            DLinkedNode* node = cache[key];
            node->value = value;
            moveToHead(node);
        }
    }
    //把node加到头部
    void addToHead(DLinkedNode* node){
        node->prev = head;
        node->next = head->next;
        head->next->prev = node;
        head->next = node;
    }
    //删掉node
    void removeNode(DLinkedNode* node){
        node->prev->next = node->next;
        node->next->prev = node->prev;
    }
    //删掉node并加到头部
    void moveToHead(DLinkedNode* node){
        removeNode(node);
        addToHead(node);
    }
    //删掉尾部节点并返回
    DLinkedNode* removeTail(){
        DLinkedNode* node = tail->prev;
        removeNode(node);
        return node;
    }
};

/**
 * Your LRUCache object will be instantiated and called as such:
 * LRUCache* obj = new LRUCache(capacity);
 * int param_1 = obj->get(key);
 * obj->put(key,value);
 */