leetcode 146. LRU Cache ----- java

esign 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.

第一次遇到的设计的题目

其实就是简单实现LRU即Least Recently Used 近期最少使用算法。

1、使用了HashMap和ArrayList

public class LRUCache {

    int size,num;
    List<Integer> list ;
    Map<Integer,Integer> map;

    public LRUCache(int capacity) {

        size = capacity;
        num = 0;
        list = new ArrayList<Integer>();
        map = new HashMap<Integer,Integer>();

    }

    public int get(int key) {
        if( map.containsKey(key) ){
            list.remove((Integer)key);
            list.add(key);
            return map.get(key);
        }
        else
            return -1;

    }

    public void set(int key, int value) {

        if( map.containsKey(key) ){
            list.remove((Integer)key);
            map.put(key,value);
            list.add(key);
        }else{
            if( num == size ){
                map.remove(list.get(0));
                list.remove((int)0);
                map.put(key,value);
                list.add(key);
            }else{
                map.put(key,value);
                list.add(key);
                num++;
            }
        }

    }
}

2、使用LinkedHashMap.

public class LRUCache {

　　 int size,num;

    Map<Integer,Integer> map;

    public LRUCache(int capacity) {

        size = capacity;

        List list =new LinkedList();

        map = new LinkedHashMap<Integer,Integer>();

    }

    public int get(int key) {

        if( map.containsKey(key) ){
            int value = map.get(key);
            map.remove(key);
            map.put(key,value);
            return value;
        }
        else
            return -1;

    }

    public void set(int key, int value) {

        if( map.containsKey(key) ){
            map.remove(key);
            map.put(key,value);
        }else{
            if( num == size ){
                int firstKey = map.keySet().iterator().next();
                map.remove(firstKey);
                map.put(key,value);
            }else{
                map.put(key,value);
                num++;
            }
        }

    }

}

3、可以使用双向链表实现。