java 手写LruCache

import java.util.*;

/**
* LruCache
*/
public class Solution {

    public static class Node{
        public int key;
        public int value;
        public Node pre;
        public Node next;

        public Node(int key, int value) {
            this.key = key;
            this.value = value;
        }
    }

    private int capacity;
    private int size = 0;
    private HashMap<Integer, Node> list = new HashMap<>();
    private Node head = new Node(-1, -1);
    private Node tail = new Node(-2, -2);

    public Solution(int capacity) {
        // write code here
        this.capacity = capacity;
        head.next = tail;
        tail.pre = head;
    }

    public int get(int key) {
        // write code here
        if (list.containsKey(key)) {
            Node node = list.get(key);
            removeNode(node);
            moveToHead(node);
            return node.value;
        } else {
            return -1;
        }
    }

    //删除节点
    private void removeNode(Node node) {
        node.pre.next = node.next;
        node.next.pre = node.pre;
    }

    //移动到队首
    private void moveToHead(Node node) {
        head.next.pre = node;
        node.next = head.next;
        node.pre = head;
        head.next = node;
    }

    
    public void set(int key, int value) {
        // write code here
        if (list.containsKey(key)) {
            Node node = list.get(key);
            node.value = value;
            //需要先删除结点
            removeNode(node);
            //再移动到队首
            moveToHead(node);
        } else {
            Node node = new Node(key, value);
            list.put(key, node);
            moveToHead(node);
            size++;
            if (size > capacity) {
                removeTail();
                size--;
            }
        }
    }

    //删除队尾
    private void removeTail() {
        Node node = tail.pre;
        list.remove(node.key);
        tail.pre.pre.next = tail;
        tail.pre = tail.pre.pre;
    }

    public static void main(String[] args) {
        Solution s = new Solution(2);
        s.set(1, 1);
        s.set(2, 2);
        System.out.println("get(1) : " + s.get(1));
        s.set(3, 3);
        System.out.println("get(2) : " + s.get(2));
        s.set(4, 4);
        System.out.println("get(1) : " + s.get(1));
        System.out.println("get(3) : " + s.get(3));
        System.out.println("get(4) : " + s.get(4));

    }
}