设计数据结构之LRU缓存

leetcode 146. LRU Cache

class LRUCache {
private:
    struct Node {

        int key;
        int val;

        Node* prev;
        Node* next;

        Node(int k, int v):key(k), val(v), prev(NULL), next(NULL){}
        Node() = default;
    };

    void removeLastNode(){
        auto last = tail->prev;
        last->prev->next = tail;
        tail->prev = last->prev;
        cache.erase(last->key);
        delete last;
    }

    void insertHead(Node* node){

        node->next = head->next;
        head->next->prev = node;
        head->next = node;
        node->prev = head;
    }

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

    Node* head;
    Node* tail;
    int cap;
    unordered_map<int, Node*> cache;
public:
    LRUCache(int capacity) {
        head = new Node;
        tail = new Node;
        head->next = tail;
        tail->prev = head;
        cap = capacity;
    }

    int get(int key) {
        if(cache.find(key) == cache.end()) return -1;
        detachNode(cache[key]);
        insertHead(cache[key]);
        return cache[key]->val;
    }

    void put(int key, int value) {
        if(cache.find(key) != cache.end()){
            cache[key]->val = value;
            detachNode(cache[key]);
        } else {
            Node* newNode = new Node(key, value);
            if(cache.size() == cap) removeLastNode();
            cache[key] = newNode;
        }
        insertHead(cache[key]);
    }
};

/**
 * 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);
 */