Problem:
Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and set.
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 should
invalidate the least recently used item before inserting a new item.
Analyze:
Code:
import java.util.HashMap;
public class LRUCache {
public LRUCache(int capacity) {
this.capacity = capacity;
this.cacheList = new CacheNodeList(capacity);
this.cacheMap = new HashMap<Integer, CacheNode>();
}
public int get(int key) {
CacheNode request = cacheMap.get(key);
if( request == null ) return -1;
cacheList.shiftToFirst(request);
return request.val;
}
public void set(int key, int value) {
if( cacheMap.containsKey(key) ){
CacheNode request = cacheMap.get(key);
request.val = value;
cacheList.shiftToFirst(request);
}
else{
if( cacheMap.size() == capacity ){
CacheNode node = cacheList.removeLast();
cacheMap.remove(node.key);
}
CacheNode newCache = new CacheNode(key, value);
cacheList.insertFirst(newCache);
cacheMap.put(key, newCache);
}
}
private int capacity;
private CacheNodeList cacheList;
private HashMap<Integer, CacheNode> cacheMap;
private class CacheNodeList {
private CacheNodeList(int capacity){
head = new CacheNode(0,0);
tail = new CacheNode(0,0);
head.next = tail;
tail.prev = head;
}
private void insertFirst(CacheNode node){
node.next = head.next;
head.next.prev = node;
head.next = node;
node.prev = head;
}
private CacheNode removeLast( ){
CacheNode lastNode = tail.prev;
tail.prev = tail.prev.prev;
tail.prev.next = tail;
return lastNode;
}
private void shiftToFirst( CacheNode node ){
node.prev.next = node.next;
node.next.prev = node.prev;
this.insertFirst(node);
}
private CacheNode head;
private CacheNode tail;
}
private class CacheNode {
int key;
int val;
CacheNode prev;
CacheNode next;
private CacheNode( int key, int val ){
this.key = key;
this.val = val;
this.prev = null;
this.next = null;
}
}
}
原文：http://www.cnblogs.com/xintongxia/p/3538171.html