/**
 * Created by kangkaisen on 16/5/4.
 * 关键点：
 * 1. 通过一个hashmap记录每个key访问情况
 * 2. key访问情况可用用HitRate
 * 3. HitRate中除了记录访问次数，还要key对象，用于反向索引查询key，清理hashmap
 * 4. HitRate中lastTime用于访问次数相同时的比较
 */
import java.util.*;

public class LFUCache {
    private static final int DEFAULT_MAX_SIZE = 3;
    private int capacity = DEFAULT_MAX_SIZE;
    //保存缓存的访问频率和时间
    private final Map<Integer, HitRate> cache = new HashMap<Integer, HitRate>();
    //保存缓存的KV
    private final Map<Integer, Integer> KV = new HashMap<Integer, Integer>();

    // @param capacity, an integer
    public LFUCache(int capacity) {
        this.capacity = capacity;
    }

    // @param key, an integer
    // @param value, an integer
    // @return nothing
    public void set(int key, int value) {
        Integer v = KV.get(key);
        if (v == null) {
            if (cache.size() == capacity) {
                Integer k = getKickedKey();
                KV.remove(k);
                cache.remove(k);
            }
            cache.put(key, new HitRate(key, 1, System.nanoTime()));
        } else { //若是key相同只增加频率,更新时间,并不进行置换
            HitRate hitRate = cache.get(key);
            hitRate.hitCount += 1;
            hitRate.lastTime = System.nanoTime();
        }
        KV.put(key, value);
    }

    public int get(int key) {
        Integer v = KV.get(key);
        if (v != null) {
            HitRate hitRate = cache.get(key);
            hitRate.hitCount += 1;
            hitRate.lastTime = System.nanoTime();
            return v;
        }
        return -1;
    }
    // @return 要被置换的key
    private Integer getKickedKey() {
        HitRate min = Collections.min(cache.values());
        return min.key;
    }

    class HitRate implements Comparable<HitRate> {
        Integer key;
        Integer hitCount; // 命中次数
        Long lastTime; // 上次命中时间

        public HitRate(Integer key, Integer hitCount, Long lastTime) {
            this.key = key;
            this.hitCount = hitCount;
            this.lastTime = lastTime;
        }

        public int compareTo(HitRate o) {
            int hr = hitCount.compareTo(o.hitCount);
            return hr != 0 ? hr : lastTime.compareTo(o.lastTime);
        }
    }

    public static void main(String[] as) throws Exception {
        LFUCache cache = new LFUCache(3);
        cache.set(2, 2);
        cache.set(1, 1);

        System.out.println(cache.get(2));
        System.out.println(cache.get(1));
        System.out.println(cache.get(2));

        cache.set(3, 3);
        cache.set(4, 4);

        System.out.println(cache.get(3));
        System.out.println(cache.get(2));
        System.out.println(cache.get(1));
        System.out.println(cache.get(4));

    }
}

import java.util.HashMap;

/**
 * Created by kangkaisen on 16/5/5.
 */

//实现起来比较简单. 维护一个链表,每次数据新添加或者有访问时移动到链表尾,
//每次淘汰数据则是淘汰链表头部的数据.
//也就是最近最少访问的数据在链表头部,最近刚访问的数据在链表尾部    

public class LRUCache {
    private class Node{
        Node prev;
        Node next;
        int key;
        int value;

        public Node(int key, int value) {
            this.key = key;
            this.value = value;
            this.prev = null;
            this.next = null;
        }
    }

    private int capacity;
    private HashMap<Integer, Node> hs = new HashMap<Integer, Node>();
    private Node head = new Node(-1, -1);
    private Node tail = new Node(-1, -1);
    // @param capacity, an integer
    public LRUCache(int capacity) {
        // write your code here
        this.capacity = capacity;
        tail.prev = head;
        head.next = tail;
    }

    // @return an integer
    public int get(int key) {
        // write your code here
        if( !hs.containsKey(key)) {
            return -1;
        }

        // remove current
        Node current = hs.get(key);
        current.prev.next = current.next;
        current.next.prev = current.prev;

        // move current to tail
        move_to_tail(current);

        return hs.get(key).value;


    }

    // @param key, an integer
    // @param value, an integer
    // @return nothing
    public void set(int key, int value) {
        // write your code here
        if( get(key) != -1) {
            hs.get(key).value = value;
            return;
        }

        if (hs.size() == capacity) {
            hs.remove(head.next.key);
            head.next = head.next.next;
            head.next.prev = head;
        }

        Node insert = new Node(key, value);
        hs.put(key, insert);
        move_to_tail(insert);
    }

    private void move_to_tail(Node current) {
        current.prev = tail.prev;
        tail.prev = current;
        current.prev.next = current;
        current.next = tail;
    }

    public static void main(String[] as) throws Exception {
        LRUCache cache = new LRUCache(3);
        cache.set(2, 2);
        cache.set(1, 1);

        System.out.println(cache.get(2));
        System.out.println(cache.get(1));
        System.out.println(cache.get(2));

        cache.set(3, 3);
        cache.set(4, 4);

        System.out.println(cache.get(3));
        System.out.println(cache.get(2));
        System.out.println(cache.get(1));
        System.out.println(cache.get(4));

    }
}