LeetCode LRU Cache (implemented in Java)

LeetCode LRU Cache (implemented in Java)

LRU Cache

Question requirements

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

get(key)-Get the value (will always be positive) of the key if the key exists in the cache, otherwise return-1.
set(key, value)-Set or insert the value if the key is not already present. When the cache reached its capacity, it shocould invalidate the least recently used item before inserting a new item.

Refer to the two blogs

Http://blog.csdn.net/beiyeqingteng/article/details/7010411

Http://gogole.iteye.com/blog/692103

It is worth mentioning that LruCache is very effective for caching images on the Android platform. for the official implementation of LruCache, refer

Http://blog.csdn.net/linghu_java/article/details/8574102

In fact, LruCache does not do anything special. It only provides LinkedHashMap with a layer. What truly implements the lru algorithm is LinkedHashMap.

During the interview, the interviewer may not like you to use javashashmap.

import java.util.Hashtable;public class LRUCache {    int capacity;    int size;    CacheNode first;    CacheNode last;    Hashtable
 
   nodes = new Hashtable
  
   ();    class CacheNode{        CacheNode prev;        CacheNode next;        int key;        int value;            }        public LRUCache(int capacity) {        this.capacity = capacity;    }        public int get(int key) {        CacheNode node = nodes.get(key);        if (node == null)            return -1;        moveToHead(node);        return node.value;    }        public void set(int key, int value) {        CacheNode node = nodes.get(key);        if (node == null){            if (size >= capacity){                if (last != null){                    nodes.remove(last.key);                }                removeLast();            }else{                ++size;            }            node = new CacheNode();        }        node.key = key;        node.value = value;        moveToHead(node);        nodes.put(key, node);    }    private void removeLast(){        if (last != null){            if (last.prev != null){                last.prev.next = null;            }else{                first = null;            }            last = last.prev;        }    }    private void moveToHead(CacheNode node){        if (node == first)            return;        if (node.prev != null)            node.prev.next = node.next;        if (node.next != null)            node.next.prev = node.prev;        if (last == node)            last = node.prev;         if (first != null){                         first.prev = node;         }         node.next = first;         first = node;         node.prev = null;         if (last == null)             last = first;    }}