LeetCode-146.LRU Cache

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

使用Java的LinkedHashMap实现

class LRUCache {//mytip
    LinkedHashMap<Integer,Integer> lru;
    int cap = 0;
    
    public LRUCache(int capacity) {
        //构造函数 accessOrder = true表示按照访问次序，为false表示按照插入次序
        lru=new LinkedHashMap<Integer,Integer>(0,0.75f,true){

            @Override
            protected boolean removeEldestEntry(Map.Entry<Integer, Integer> eldest) {
                return size()>cap;
            }

        };
        cap = capacity;
    }
    
    public int get(int key) {
        Integer re = lru.get(key);
        return null==re?-1:re;
    }
    
    public void put(int key, int value) {
        lru.put(key,value);
    }
}

自己实现Map+双向链表

class LRUCache {
    Map<Integer,Node> map;
    int cap=0;
    Node head =null;
    Node tail = null;
    
    public LRUCache(int capacity) {
        map = new HashMap<>();
        cap = capacity;
        head = new Node(0,0);
        tail = new Node(0,0);
        head.next =tail;
        tail.pre =head;
    }
    
    public int get(int key) {
        Node node = map.get(key);
        if(null!=node){
            nodeToHead(node);
            return node.value;
        }
        return -1;
    }
    
    public void put(int key, int value) {
        Node node = map.get(key);
        if(null!=node){
            node.value = value;
            nodeToHead(node); 
            return ;
        }
        if(map.size()==cap){
            node  = tail.pre;
            node.pre.next = tail;
            tail.pre = node.pre;
            map.remove(node.key);
        }
        node = new Node(key,value);
        node.next = head.next;
        node.pre = head;
        head.next = node;
        node.next.pre = node;
        map.put(key,node);
        
    }
    
    private void nodeToHead(Node node){
        node.pre.next = node.next;
        node.next.pre = node.pre;
        node.next = head.next;
        node.pre = head;
        node.next.pre =node;
        head.next = node;
    }
}

class Node{
    int key;
    int value;
    Node pre;
    Node next;
    public Node(int key,int value){
        this.key= key;
        this.value  =value;
        pre = null;
        next = null;
    }
}