leetcode 146. LRU Cache 需要深入学习Java的Map的内部实现

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

get(key) - Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.
put(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.

Follow up:
Could you do both operations in O(1) time complexity?

Example:

LRUCache cache = new LRUCache( 2 /* capacity */ );

cache.put(1, 1);
cache.put(2, 2);
cache.get(1); // returns 1
cache.put(3, 3); // evicts key 2
cache.get(2); // returns -1 (not found)
cache.put(4, 4); // evicts key 1
cache.get(1); // returns -1 (not found)
cache.get(3); // returns 3
cache.get(4); // returns 4

我也是网上参考的教程。

强烈建议学习深入Java集合学习系列：HashMap的实现原理和深入Java集合学习系列：LinkedHashMap的实现原理。

代码如下：

import java.util.HashMap;import java.util.LinkedHashMap;/* * http://blog.csdn.net/HE19930303/article/details/51315263 *  * http://zhangshixi.iteye.com/blog/673789  *  * http://zhangshixi.iteye.com/blog/672697 *  * 这个题值得学习Java中的HashMap和LinkedHashMap * */public class LRUCache extends LinkedHashMap<Integer,Integer>{    private int maxcapacity;    public LRUCache(int capacity)     {        super(capacity,0.75f,true);        this.maxcapacity=capacity;    }    public int get(int key)     {        Integer vaule=super.get(key);        if(vaule==null)return -1;        else return vaule;    }    public void set(int key, int value)     {        super.put(key,value);    }    protected boolean removeEldestEntry(Map.Entry<Integer,Integer> eldest)    {        return size()>maxcapacity;    }}/** * 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); */