LRU cache

浏览数：15 / 时间：2015年06月20日

实现lru 缓存

思路：用map+链表实现，map用来提高查询速度，链表用来存放元素。链表头放入最新的元素，表尾为最老元素。访问cache命中，或者cache满写入时都需要对链表内容和map进行调整。

JDK里面有一个LinkedHashMap就是基于这个思路实现的。

LRU Cache

Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and set.

get(key) - Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.
set(key, value) - Set or insert the value if the key is not already present. When the cache reached its capacity, it should invalidate the least recently used item before inserting a new item.

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public class LRUCache {
    static class Node {
        int key;
        int value;


        @Override
        public String toString() {
            return "Node{" +
                    "key=" + key +
                    ", value=" + value +
                    '}';
        }
    }


    static private LinkedList<Node> cache;
    static private int cap;
    static private Node indexMap[];

    public LRUCache(int capacity) {
        cache = new LinkedList<Node>();
        indexMap = new Node[100000];
        cap = capacity;
    }

    static public boolean isFull() {
        return cache.size() == cap;
    }

    static public Node find(int key) {
        if (cache.isEmpty())
            return null;
        Node tar = null;

        if ((tar = indexMap[key]) == null)
            return null;

        cache.remove(tar);
        cache.addFirst(tar);
        return tar;

    }

     public int get(int key) {
        Node node = find(key);
        if (node == null) {
            return -1;
        }
        return node.value;
    }

     public void set(int key, int value) {
        Node node = null;
        if ((node = find(key)) != null) {
            node.value = value;
            return;
        }

        //not find the element

        if (isFull()) {
            indexMap[cache.getLast().key] = null;
            cache.removeLast();
        }


        Node newNode = new Node();
        newNode.key = key;
        newNode.value = value;
        cache.addFirst(newNode);
        indexMap[key] = newNode;

    }
}

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LRU cache