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

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本文介绍了一种使用Java实现的LRU缓存数据结构。该缓存支持get和put操作，并能在达到容量限制时移除最久未使用的项。通过继承LinkedHashMap并调整其行为来实现高效的数据管理和访问。

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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.youkuaiyun.com/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);
 */