Leetcode Hot100 第18题 146.LRU缓存

struct Node{
    int key,value;
    Node *prev,*next;
    Node(): key(0),value(0),prev(nullptr),next(nullptr) {}
    Node(int _key, int _value): key(_key),value(_value),prev(nullptr),next(nullptr) {}
};
class LRUCache {
public:
    int capacity,size;
    Node *head, *tail;
    unordered_map<int,Node*> cache;
    LRUCache(int _capacity) {
        capacity = _capacity;
        size = 0;
        head = new Node();
        tail = new Node();
        head->next = tail;
        tail->prev = head;
    }
    
    int get(int key) {
        if(cache.count(key)){
            Node* node = cache[key];
            removeNode(node);
            addNodeTohead(node);
            return node->value;
        }
        return -1;
    }
    
    void put(int key, int value) {
        if(cache.count(key)){
            Node* node = cache[key];
            removeNode(node);
            addNodeTohead(node);
            node->value = value;
        }else{
            if(size==capacity){
                Node* node = tail->prev;
                removeNode(node);
                cache.erase(node->key);
                delete node;
                size--;
            }
            Node* node = new Node(key,value);
            addNodeTohead(node);
            cache[key]=node;
            size++;
        }
    }

    void removeNode(Node *node){
        node->prev->next = node->next;
        node->next->prev = node->prev;
    }

    void addNodeTohead(Node *node){
        node->next = head->next;
        node->prev = head;
        head->next->prev = node;
        head->next = 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);
 */