LRUCache.java

package com.interview.linklist;

import java.util.HashMap;
import java.util.Map;

/**
 * http://www.geeksforgeeks.org/implement-lru-cache/
 * Test cases:
 * MAX_SIZE greater than 1
 * Delete when empty
 * Delete when full
 * Enter data more than max
 * Delete till cache is empty
 */
public class LRUCache {

    private Node head;
    private Node tail;
    private Map<Integer,Node> map = new HashMap<Integer,Node>();
    private int MAX_SIZE = 5;
    private int size = 0;
    public LRUCache(int size){
        MAX_SIZE = size;
    }
    
    public void used(int data){
        if(containsInCache(data)){
            Node node = map.get(data);
            if(node != head){
                deleteFromCache(data);
                node.next = head;
                head.before = node;
                head = node;
                map.put(data, node);
            }
        }else{
            addIntoCache(data);
        }
    }
    
    public void addIntoCache(int data){
        size++;
        if(head == null){
            head = Node.newNode(data);
            tail = head;
            return;
        }
        if(size > MAX_SIZE){
            tail = tail.before;
            Node next = tail.next;
            tail.next = null;
            next.before = null;
            map.remove(next.data);
        }
        Node newNode = Node.newNode(data);
        newNode.next = head;
        if(head != null){
            head.before = newNode;
        }
        head = newNode;
        map.put(data, newNode);
        return;
    }
    
    public void printCache(){
        Node temp = head;
        while(temp != null){
            System.out.print(temp.data + " ");
            temp = temp.next;
        }
        System.out.println();
    }
    
    public boolean containsInCache(int data)
    {
        return map.containsKey(data);
    }
    
    public void deleteFromCache(int data){
        Node node = map.get(data);
        if(node == null){
            return;
        }
        map.remove(data);
        if(size == 1){
            head = null;
            tail = null;
        }
        else if(node == head){
            head = head.next;
            if(head != null){
                head.before = null;
            }
            node.next = null;
        }else if(node == tail){
            tail = tail.before;
            tail.next = null;
        }else{
            Node before = node.before;
            Node next = node.next;
            before.next = next;
            next.before = before;
        }
    }

    public static void main(String args[]){
        LRUCache lruCache = new LRUCache(5);
        lruCache.used(4);
        
        lruCache.used(5);
        lruCache.printCache();
        lruCache.used(6);
        lruCache.printCache();
        lruCache.used(5);
        lruCache.printCache();
        lruCache.used(9);
        lruCache.printCache();
        lruCache.used(10);
        lruCache.printCache();
        lruCache.used(11);
        lruCache.printCache();
        lruCache.used(16);
        lruCache.printCache();
        lruCache.used(10);
        lruCache.printCache();
        lruCache.deleteFromCache(10);
        lruCache.printCache();
        lruCache.deleteFromCache(9);
        lruCache.printCache();
    }
}