leetcode_Design and implement a data structure for Least Recently Used (LRU) cache_design a data structure for lru cache-优快云博客

本文介绍了一种最少最近使用（LRU）缓存的数据结构设计与实现方法，通过使用LinkedHashMap来维持元素的访问顺序，实现了get和set两个核心操作。文中详细解释了当缓存满载时如何替换最久未使用的项。

    /*
     * Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and set.
     * */
	public class LRUCache
	{
		
		private Map<Integer, MapNode> map = null;
		private int capacity;
		private int size;
		public LRUCache(int capacity)
		{
			this.capacity = capacity;
			size = 0;
			map = new LinkedHashMap<Integer,MapNode>();
		}

		public int get(int key)
		{
			if(map.containsKey(key) == false)
			{
				return -1;
			}
			else 
			{
				int r = map.get(key).value;
				
				//adjust the position of this item
				MapNode tmMapNode = map.get(key);
				map.remove(key);
				map.put(key, tmMapNode);
				return r;
			}
		}

		public void set(int key, int value)
		{
			if(map.containsKey(key)==false)
			{
				if(size<capacity)
				{
					map.put(new Integer(key), new MapNode(key, value));
					size++;					
				}
				else 
				{
					//if size capacity is zero , does this still work correctly?
					//delete the first one which is the least used one
					Iterator<Entry<Integer, MapNode>> iterator= map.entrySet().iterator();
					Integer tmp = null;
					if(iterator.hasNext())
					{
						tmp = iterator.next().getKey();
//						map.remove(tmp); 
//						map.put(new Integer(key), new MapNode(key, value)); 
					}
					if(tmp != null)
					{
						map.remove(tmp); 
						map.put(new Integer(key), new MapNode(key, value)); 
					}
					
				}
			}
			else 
			{
				//delete this node and change its content then add it,make it the last one
				MapNode tmpMapNode =  map.get(new Integer(key));
				map.remove(new Integer(key));
				tmpMapNode.value = value;
				map.put(new Integer(key), tmpMapNode);
			}
		}
		
		public class MapNode
		{
			int key;
			int value;
			public MapNode(int k, int v)
			{
				key = k;
				value = v;
			}
		}
	}

总结延伸://各种容器使用 map hashmap 等他们操作的复杂度?，这里使用的LinkedHashMap其中数据保持插入顺序，后进的在头部

(notice that java.util.LinkedHashMap uses insertion-order.)