LeetCode：146LRU缓存

class LRUCache {

    //定义双向链表的节点结构
    class Node{
        int key;
        int value;
        Node prev;
        Node next;
        public Node(){};
        public Node(int key, int value){
            this.key = key;
            this.value = value;
        }
    }

    private Map<Integer,Node> cache = new HashMap<>();
    private int capacity;
    private int size;
    //头尾节点
    private Node head,tail;

    public LRUCache(int capacity) {
        this.capacity = capacity;
        this.size = 0;
        //初始化头尾
        head = new Node();
        tail = new Node();
        head.next = tail;
        tail.prev = head;
    }
    //获取
    public int get(int key){
        Node node = cache.get(key);
        if(node == null){
            return -1;
        }
        moveToHead(node);
        return node.value;
    }
    //放入/更新
    public void put(int key, int value){
        Node node = cache.get(key);

        if(node == null){
            //全新的数据
            Node newNode = new Node(key,value);
            cache.put(key,newNode);
            addToHead(newNode);
            size++;
            //判断是否已满
            if(size > capacity){
                Node tailNode = removeTail();
                cache.remove(tailNode.key);
                size--;
            }
        }else{
            //更新数据
            node.value = value;
            moveToHead(node);
        }
    }
    //将一个节点抽出来，插到最前面（现有节点）
    private void moveToHead(Node node){
        removeNode(node);
        addToHead(node);
    }
    //将一个节点从现有位置取出来
    private void removeNode(Node node){
        node.prev.next = node.next;
        node.next.prev = node.prev;
    }
    //放到最前面
    private void addToHead(Node node){
        node.prev = head;
        node.next = head.next;
        head.next.prev = node;
        head.next = node;
    }
    //逐出最久未使用的关键字
    private Node removeTail(){
        Node res = tail.prev;
        removeNode(res);
        return res;
    }
}

/**
 * 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);
 */

哈希表+双向链表的组合结构

写几个方法方便直接调用：

将一个节点直接插入到最前面的方法

将一个节点从当前位置取出来的方法

接节点抽出来放到最前面的方法

丢掉最久未使用的关键字的方法