手撕LRU算法

import java.util.HashMap;
import java.util.Map;

class Node {
    int k, v;
    Node l, r;

    Node(int _k, int _v) {
        k = _k;
        v = _v;
    }
}

public class LRUcache {

    int n;
    Node head, tail;
    Map<Integer, Node> map;

    public LRUcache(int capacity) {
        n = capacity;
        map = new HashMap<>();
        head = new Node(-1, -1);
        tail = new Node(-1, -1);
        head.r = tail;
        tail.l = head;
    }

    public int get(int key) {
        if (map.containsKey(key)) {
            Node node = map.get(key);
            refresh(node);
            return node.v;
        }
        return -1;
    }

    public void put(int key, int value) {
        Node node = null;
        if (map.containsKey(key)) {
            node = map.get(key);
            node.v = value;
        } else {
            if (map.size() == n) {
                Node del = tail.l;
                map.remove(del.k);
                delete(del);
            }
            node = new Node(key, value);
            map.put(key, node);
        }
        refresh(node);
    }


    void refresh(Node node) {
        delete(node);
        node.r = head.r;
        node.l = head;
        head.r.l = node;
        head.r = node;
    }


    void delete(Node node) {
        if (node.l != null) {
            Node left = node.l;
            left.r = node.r;
            node.r.l = left;
        }
    }

    public static void main(String[] args) {
        LRUcache lrUcache = new LRUcache(5);
        lrUcache.put(12, 34);
        System.out.println(lrUcache.get(12));
        System.out.println(lrUcache.head.k);
    }
}