面试题：实现LRUCache：：Least Recently Used的缩写,意思是最近最少使用,它是一种Cache替换算法

package com.Netesay.interview;

import java.util.HashMap;
import java.util.Map;

/**
 * @Author: weblee
 * @Email: likaiweb@163.com
 * @Blog: http://www.cnblogs.com/lkzf/
 * @Time: 2014年10月24日下午6:29:40
 * 
 *************        function description ***************
 *
 ****************************************************
 */

public class LRUCache {
    Map<Integer, CacheNode> cacheMap;
    CacheNode head, tail;
    int capacity;
    
    //使用双向链表和map，map将k对应与链表的节点  
    //链表里保存k和value  
    public LRUCache(int capacity) {
    this.capacity = capacity;
    
    cacheMap = new HashMap<Integer, CacheNode>(capacity);
    
    head = new CacheNode(-1, -1);
    tail = new CacheNode(1, 1);
    
    head.next = tail;
    tail.pre = head;
    }

    public int get(int key) {
    if (cacheMap.containsKey(key)) {
        CacheNode node = (CacheNode)cacheMap.get(key);
        
        put2Head(node);
        
        return node.value;
    } else {
        return -1;
    }
    }

    public void set(int key, int value) {
    if (cacheMap.containsKey(key)) {
        CacheNode p = cacheMap.get(key);
        
        p.value = value;
        
        put2Head(p);
    } else if(cacheMap.size() < capacity) {
        CacheNode node = new CacheNode(key, value);
        put2Head(node);
        cacheMap.put(key, node);
    } else {
        CacheNode p = new CacheNode(key, value);
        put2Head(p);
        cacheMap.put(key, p);
        
        int tmpKey = removeEnd();
        cacheMap.remove(tmpKey);
    }
    }
    
    private void put2Head(CacheNode p) {
    if (p.next != null && p.pre != null) {
        p.pre.next = p.next;
        p.next.pre = p.pre;
    }
    
    p.pre = head;
    p.next = head.next;
    head.next.pre = p;
    head.next = p;
    }
    
    private int removeEnd() {
    CacheNode p = tail.pre;
    tail.pre.pre.next = tail;
    tail.pre = p.pre;
    
    p.pre = null;
    p.next = null;
    
    return p.key;
    }
}

class CacheNode {
    int key;
    int value;
    
    CacheNode pre;
    CacheNode next;

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