LeetCode: LRU Cache [146]

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

class LRUCache{
private:
	Node* head;
	Node* tail;
	int capacity;
	map<int, Node*>cache;
public:
    LRUCache(int capacity) {
        this->head = NULL;
		this->tail = NULL;
		this->capacity = capacity;
    }
	
	void move2tail(Node* node){
		if(node==tail)return;
		if(node==head){
			head = node->next;
			head->prev=NULL;
			tail->next=node;
			node->prev=tail;
			tail=node;
			tail->next=NULL;
		}
		else{
			node->prev->next = node->next;
			node->next->prev = node->prev;
			tail->next=node;
			node->prev=tail;
			tail=node;
			tail->next=NULL;
		}
	}
    
    int get(int key) {
        if(this->cache.find(key)==this->cache.end())return -1;
		move2tail(this->cache[key]);
		return this->cache[key]->val;
    }
    
    void set(int key, int value) {
        if(this->cache.find(key)==this->cache.end()){//cache中还没有
			if(this->capacity==0){//cache已经满了
				//删除头结点
				this->cache.erase(head->key);
				head=head->next;
				if(head)head->prev=NULL;
				else tail=NULL;
			}
			else{//cache还没满
				this->capacity--;
			}
			//加入新节点
			Node* newNode=new Node(key, value);
			this->cache[key]=newNode;
			if(tail){
				tail->next=newNode;
				newNode->prev=tail;
				tail=newNode;
				tail->next=NULL;
			}
			else{
				head=tail=newNode;
			}
		}
		else{//cache中已经有了
			this->cache[key]->val = value;
			move2tail(this->cache[key]);
		}
    }
};