题目链接：https://leetcode.cn/problems/lru-cache/description/?envType=study-plan-v2&envId=top-100-liked
原理非常简单，一个双端链表配上一个hash表。
首先我们要知道什么是LRU就是最小使用淘汰。怎么淘汰，链表尾部就是最不常用的直接删除，最近使用过的就移动到链表头部。要查找就利用hash表进行映射查找。
代码：

class LRUCache {//需要定义的双端链表节点//哈希表class Node{int key;int value;Node prev;Node next;public Node() {}public Node(int _key,int _value) {key = _key;value = _value;}}private Map<Integer,Node > cache = new HashMap<>();private int size;private int capacity;private Node head,tail;public LRUCache(int capacity) {this.size = 0;this.capacity = capacity;head = new Node();tail = new Node();head.next = tail;tail.prev = head;}public int get(int key) {Node node = cache.get(key);if(node == null) return -1;moveToHead(node);return node.value;}public void put(int key, int value) {//如果存在if(cache.containsKey(key)){Node t = cache.get(key);t.value = value;moveToHead(t);}else{//如果不存在size++;if(size>capacity){cache.remove(tail.prev.key);//System.out.println(tail.prev.key);moveTail();size--;}Node node = new Node(key,value);Node temp = head.next;head.next = node;node.prev = head;temp.prev = node;node.next = temp;cache.put(key,node);}}public void moveToHead(Node node){//本身删除了Node qian = node.prev;qian.next = node.next;node.next.prev = qian;//再插到头部Node temp = head.next;head.next = node;node.prev = head;temp.prev = node;node.next = temp;}public void moveTail(){Node temp = tail.prev.prev;temp.next = tail;tail.prev = temp;}
}/*** Your LRUCache object will be instantiated and called as such:* LRUCache obj = new LRUCache(capacity);* int param_1 = obj.get(key);* obj.put(key,value);*/