leetcode146. LRU缓存机制

双向链表+哈希表实现LRU

class LRUCache {
    
    public static class LinkedNode {
        int key;
        int val;
        LinkedNode prev;
        LinkedNode next;
        public LinkedNode(int key, int val) {
            this.key = key;
            this.val = val;
        }
    }

    Map<Integer, LinkedNode> map;
    LinkedNode head;
    LinkedNode tail;
    int capacity;
    int count;
    
    public LRUCache(int capacity) {
        map = new HashMap<>();
        head = new LinkedNode(0, 0);
        tail = new LinkedNode(0, 0);
        head.next = tail;
        tail.prev = head;
        this.capacity = capacity;
        count = 0;
    }
    
    // 移除尾结点前面的节点
    public void removeTail() {
        if (tail.prev == head) throw new IllegalArgumentException("There is no node to remove");
        LinkedNode node = tail.prev;
        tail.prev.prev.next = tail;
        tail.prev = tail.prev.prev;
    }
    
    // 将node节点添加到头结点后面
    public void addToHead(LinkedNode node) {
        node.next = head.next;
        head.next.prev = node;
        head.next = node;
        node.prev = head;
    }
    
    // 删除node节点
    public void removeNode(LinkedNode node) {
        node.prev.next = node.next;
        node.next.prev = node.prev;
    }
    
    public int get(int key) {
        if (map.containsKey(key)) {
            LinkedNode node = map.get(key);
            removeNode(node);
            addToHead(node);
            return node.val;
        }
        return -1;
    }
    
    public void put(int key, int value) {
        if (map.containsKey(key)) {
            LinkedNode node = map.get(key);
            node.val = value;
            removeNode(node);
            addToHead(node);
        } else {
            LinkedNode node = new LinkedNode(key, value);
            if (count == capacity) {              
                map.remove(tail.prev.key);
                removeTail();
                addToHead(node);
                map.put(key, node);
            } else {
                addToHead(node);
                map.put(key, node);
                count++;
            }
        }
    }
}

/**
 * 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);
 */