LRU Cache

LRU Cache

Design 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.

思路：

　　双向链表

我的代码：

public class LRUCache {

    

    public LRUCache(int capacity) {

        this.capacity = capacity;

        this.head = new Node(-1, -1);

        this.tail = new Node(-1, -1);

        head.next = tail;

        tail.pre = head;

    }

    

    public int get(int key) {

        if(!hm.containsKey(key))    return -1;

        Node node = hm.get(key);

        //remove current

        node.pre.next = node.next;

        node.next.pre = node.pre;

        moveTotail(node);

        return node.val;

    }

    

    public void set(int key, int value) {

        if(get(key) != -1)

        {

            hm.get(key).val = value;

            return;

        }

        if(hm.size() == capacity)

        {

            hm.remove(head.next.key);

            head.next = head.next.next;

            head.next.pre = head;

        }

        Node node = new Node(key,value);

        hm.put(key,node);

        moveTotail(node);

    }

    public void moveTotail(Node node){

        node.pre = tail.pre;

        node.next = tail;

        tail.pre.next = node;

        tail.pre = node;

    }

    private Node head; 

    private Node tail;

    private int capacity;

    private HashMap<Integer,Node> hm = new HashMap<Integer,Node>();

    private class Node{

        Node pre;

        Node next;

        int key;

        int val;

        public Node(int key, int val)

        {

            this.key = key;

            this.val = val;

        }

    }

}

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学习之处：

• 在做这道题的时候，一下子就想到双向链表了，由于自己觉得简单，就边看答案边做的，差评！！！
• 这道题有点眼高手低，以后不能这样！其实好长时间才AC的