Leetcode #146 LRU Cache

[yokostan]

class LRUCache {
    class ListNode {
        public int key, val;
        public ListNode next;

        public ListNode(int key, int val) {
            this.key = key;
            this.val = val;
            this.next = null;
        }
    }

    public int capacity, size;
    public ListNode dummy, tail;
    public Map<Integer, ListNode> map;

    public LRUCache(int capacity) {
        this.capacity = capacity;
        this.map = new HashMap<Integer, ListNode>();
        this.dummy = new ListNode(0, 0);
        this.tail = this.dummy;
    }

    public void moveToTail(int key) {
        ListNode prev = map.get(key);
        ListNode curr = prev.next;

        if (tail == curr) return ;

        prev.next = prev.next.next;
        tail.next = curr;

        if (prev.next != null) {
            map.put(prev.next.key, prev);
        }
        map.put(curr.key, tail);

        tail = curr;
    }

    public int get(int key) {
        if (!map.containsKey(key)) return -1;
        moveToTail(key);
        return tail.val;
    }

    public void put(int key, int value) {
        if (get(key) != -1) {
            ListNode prev = map.get(key);
            prev.next.val = value;
            return ;
        }

        if (size < capacity) {
            size++;
            ListNode curr = new ListNode(key, value);
            tail.next = curr;
            map.put(key, tail);

            tail = curr;
            return;
        }

        // replace the first node with new key, value
        ListNode first = dummy.next;
        map.remove(first.key);

        first.key = key;
        first.val = value;
        map.put(key, dummy);

        moveToTail(key);
    }
}

/**
 * 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);
 */