node類

class Node{
    private int v;
    
    private Object  k;
    private Node next;
    private Node pre;
    
    public Node(Object key,int value) {
        this.v = value;
        this.k = key;
    }
    
    public int getV() {
        return v;
    }
    public void setV(int v) {
        this
 
.v = v;
    }
    public Node getNext() {
        return next;
    }
    public void setNext(Node next) {
        this.next = next;
    }
    public Node getPre() {
        return pre;
    }
    public void setPre(Node pre) {
        this.pre = pre;
    }

    public Object getK() {
        return k;
    }

    
 
public void setK(Object k) {
        this.k = k;
    }
}

LRUcache類

public class LRUCache_NowCode {
    public static Object[] LRU(int[][] operators, int k) {
        if (operators.length <= 0 || k <= 0) {
            return null;
        }
        List<Object> reList = new ArrayList<Object>();
        LRUCache_NowCode cache 
 
= new LRUCache_NowCode(k);
        for (int[] tmpArr : operators) {
            int key = tmpArr[0];
            switch (key) {
            case 1:
                cache.set(Integer.valueOf(tmpArr[1]), Integer.valueOf(tmpArr[2]));
                break;
            case 2:
                reList.add(cache.get(Integer.valueOf(tmpArr[1])));
                break;
            default:
                break;
            }
        }
        Object[] reArr = new Object[reList.size()];
        for (int i = 0; i < reList.size(); i++) {
            reArr[i] = reList.get(i);
        }
        return reArr;
    }

    public LRUCache_NowCode(int k) {
        this.size = k;
    }

    private int size = -1; // 容量

    private Node head = null;
    private Node tail = null;

    private Map<Object, Node> cacheMap = new HashMap<Object, Node>();

    public void set(Object key, int value) {
        System.out.println("set key -> " + key + " value -> " + value);
        Node node = cacheMap.get(key);
        if (node == null) {
            node = new Node(key,value);
            cacheMap.put(key, node);
        } else {
            // 將節點從連結串列中移除
            if (node.getNext() != null) {
                node.getNext().setPre(node.getPre());
            }
            if (node.getPre() != null) {
                node.getPre().setNext(node.getNext());
            }
            node.setV(value);
        }
        // 頭尾節點給預設值
        if (head == null || tail == null) {
            head = tail = node;
        }
        // 容量判斷
        if (cacheMap.size() > size) {
            //移除尾指標
            cacheMap.remove(tail.getK());
            //移動尾指標
            tail = tail.getPre();
            tail.setNext(null);
        }
        // 當前節點不是頭結點
        if (head != node) {
            head.setPre(node);
            node.setNext(head);
            node.setPre(null);
            head = node;
        }
        printHead(head);
        printTail(tail);
        System.out.println("-----");
    }

    public static void printHead(Node node) {
        System.out.print(node.getV());
        Node tmp = node;
        while (tmp.getNext() != null) {
            tmp = tmp.getNext();
            System.out.print(" next -> " + tmp.getV());
        }
        System.out.println();
    }

    public static void printTail(Node node) {
        System.out.print(node.getV());
        Node tmp = node;
        while (tmp.getPre() != null) {
            tmp = tmp.getPre();
            System.out.print(" pre -> " + tmp.getV());
        }
        System.out.println();
    }

    /**
     * 移到佇列頭部
     * 
     * @param i
     * @return
     */
    public Object get(Object key) {
        System.out.println("get key -> " + key);
        Node existNode = cacheMap.get(key);
        if (existNode == null) {
            return -1;
        }
        Node n = existNode.getNext();
        Node p = existNode.getPre();
        if (p != null) {
            p.setNext(n);
        }
        if (n != null) {
            n.setPre(p);
        }
        existNode.setNext(head);
        head.setPre(existNode);
        existNode.setPre(null);
        head = existNode;
        // 如果恰好查的是尾節點，那將尾指標前移一個單位
        if (tail == existNode) {
            tail = p;
            tail.setNext(null);
        }
        return existNode.getV();
    }

}

main方法測試

public static void main(String[] args) {
        int[][] operators = new int[][] { 
        new int[] { 1, 1, 1 }, 
        new int[] { 1, 2, 2 }, 
        new int[] { 1, 3, 2 },
    new int[] { 2, 1 }, 
        new int[] { 1, 4, 4 }, 
        new int[] { 2, 2 } };
    Object[] arr = LRUCache_NowCode.LRU(operators, 3);
    System.out.println(Arrays.toString(arr));
    }        

此處直接將key儲存在了物件中，可以根據物件之間的引用關係直接找到前後的key，簡化處理頭尾節點時邏輯。