LRU 缓存

LRU的定义

LRU是Least Recently Used的缩写，即最近最少使用，是一种常用的页面置换算法，选择最近最久未使用的页面予以淘汰。该算法赋予每个页面一个访问字段，用来记录一个页面自上次被访问以来所经历的时间 t，当须淘汰一个页面时，选择现有页面中其 t 值最大的，即最近最少使用的页面予以淘汰。

实现类

class LRUCache {
    class Node {
        int key;
        int value;
        Node prev;
        Node next;
        Node() {

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

    private Map<Integer, Node> cache;
    private Node head;
    private Node tail;
    private int capacity;
    private int size;

    public LRUCache(int capacity) {
        cache = new HashMap<>();
        this.capacity = capacity;
        head = new Node();
        tail = new Node();
        head.next = tail;
        tail.prev = head;
    }

    public int get(int key) {
        if (!cache.containsKey(key)) {
            return -1;
        }
        Node node = cache.get(key);
        moveToHead(node);
        return node.value;
    }

    public void put(int key, int value) {
        if (cache.containsKey(key)) {
            Node node = cache.get(key);
            node.value = value;
            moveToHead(node);
        } else {
            Node node = new Node(key, value);
            cache.put(key, node);
            addToHead(node);
            ++size;
            if (size > capacity) {
                node = removeTail();
                cache.remove(node.key);
                --size;
            }
        }
    }

    private void moveToHead(Node node) {
        removeNode(node);
        addToHead(node);
    }

    private void removeNode(Node node) {
        node.prev.next = node.next;
        node.next.prev = node.prev;
    }

    private void addToHead(Node node) {
        node.next = head.next;
        head.next.prev = node;
        head.next = node;
        node.prev = head;
    }

    private Node removeTail() {
        Node node = tail.prev;
        removeNode(node);
        return node;
    }
}

复制代码

使用

/**
 * 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);
 */
复制代码