algorithm/LRU_Cache.java at master · cookiecooker/algorithm · GitHub

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public class LRUCache {

    int size;
    int capacity;
    HashMap<Integer,Node> map;
    Node first;
    Node last;


    public LRUCache(int capacity) {

       this.capacity = capacity;
       size = 0;
       map = new HashMap<Integer,Node>();
    }

    public int get(int key) {

       Node node = map.get(key);
       if(node == null) return -1;
       else{
           moveTohead(node);
           return node.val;
       }
    }

    public void set(int key, int value) {

        Node node = map.get(key);

        if(node == null){

            if(size == capacity){
                map.remove(last.key);
                removelast();
            }
            else size++;

            node = new Node(key,value);
        }

        if(size == 1)  first = last = node;

        node.val = value;
        moveTohead(node);
        map.put(key,node);
    }

    public void moveTohead(Node node){

        if(node == first) return;

        if(node.pre != null)node.pre.next = node.next;
        if(node.next != null)node.next.pre = node.pre;

        if(node == last) last = node.pre;

        if(first != null)   first.pre = node;
        node.pre = null;
        node.next = first;
        first = node;
    }

    public void removelast(){

       if(last != null){

           if(last.pre != null) last.pre.next = last.next;
           else first = null;

           last = last.pre;
       }
    }

}

class Node{

    public int key;
    public int val;
    public Node pre;
    public Node next;

    public Node(int key, int val){

        this.key = key;
        this.val = val;
    }

}