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

灰太狼 2022-06-08 06:24 106阅读 0赞

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][Java_HashMap]和[深入Java集合学习系列：LinkedHashMap的实现原理][Java_LinkedHashMap]。

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);
     */

[Java_HashMap]: http://zhangshixi.iteye.com/blog/672697
[Java_LinkedHashMap]: http://zhangshixi.iteye.com/blog/673789