LRU缓存，Java 代码

class LRUCache {
    class LinkedNode {
        Integer key;
        Integer value;
        LinkedNode prev;
        LinkedNode next;
        LinkedNode (Integer key, Integer value) {
            this.key = key;
            this.value = value;
        }
        LinkedNode () {
        }
        LinkedNode (Integer key, Integer value, LinkedNode prev, LinkedNode next) {
            this.key = key;
            this.value = value;
            this.prev = prev;
            this.next = next;
        }
    }
    private Integer capacity;
    private LinkedNode head;
    private LinkedNode tail;

    private Map<Integer, LinkedNode> cache = new HashMap<>();

    public LRUCache(int capacity) {
        this.capacity = capacity;
        this.tail = new LinkedNode();
        this.head = new LinkedNode();
        tail.prev = head;
        head.next = tail;
    }

    public int get(int key) {
        if (cache.get(key) == null) {
            return -1;
        }
        LinkedNode node = cache.get(key);
        moveToHead(node);
        return node.value;
    }

    public void put(int key, int value) {
        if (cache.containsKey(key)) {
            LinkedNode node = cache.get(key);
            node.value = value;
            moveToHead(node);
            return;
        }
        if (cache.size() >= capacity) {
            LinkedNode node = removeTail();
            cache.remove(node.key);
        }
        LinkedNode node = new LinkedNode(key, value);
        addToHead(node);
        cache.put(key, node);
    }
    private void removeNode(LinkedNode node) {
        node.next.prev = node.prev;
        node.prev.next = node.next;
    }
    private void moveToHead(LinkedNode node) {
        removeNode(node);
        addToHead(node);
    }
    private void addToHead(LinkedNode node) {
        head.next.prev = node;
        node.next = head.next;
        head.next = node;
        node.prev = head;
    }
    private LinkedNode removeTail() {
        LinkedNode 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);
 */