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?

cache的问题，和在15213里面写过的cache 和 malloc类似。

基本思想在于用双向链表来进行LRU的操作。

public class LRUCache {            private class Node{        int key;        int value;        Node prev;        Node next;                        public Node(int key, int value){            this.key = key;            this.value = value;        }                    }            Node head;    Node tail;    int capacity;    int size;    Map<Integer, Node> map;    public LRUCache(int capacity) {        head = new Node(0,0);        head.next = tail;                tail = new Node(0,0);        tail.prev = head;        this.capacity = capacity;        size = 0;        map = new HashMap<>(capacity);    }        public int get(int key) {        if(map.containsKey(key)){            Node tmp = map.get(key);                       tmp.prev.next = tmp.next;            tmp.next.prev = tmp.prev;            tail.prev.next = tmp;            tmp.prev = tail.prev;            tmp.next = tail;            tail.prev = tmp;            return tmp.value;        }else{            return -1;        }    }        public void put(int key, int value) {        if(!map.containsKey(key)){            if(size == capacity){                int tmpkey = head.next.key;                head.next = head.next.next;                head.next.prev = head;                map.remove(tmpkey);                size--;            }            Node tmp = new Node(key,value);            map.put(key,tmp);            tail.prev.next = tmp;            tmp.prev = tail.prev;            tmp.next = tail;            tail.prev = tmp;            size++;        }else{            Node tmp = map.get(key);            tmp.value = value;            tmp.prev.next = tmp.next;            tmp.next.prev = tmp.prev;            tail.prev.next = tmp;            tmp.prev = tail.prev;            tmp.next = tail;            tail.prev = tmp;                    }    }}/** * 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); */