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import java.util.HashMap; | |
import java.util.Map; | |
import java.util.concurrent.ConcurrentHashMap; | |
public class LRUCache { | |
public static void main(String[] args) { | |
LRUCache cache = new LRUCache(2); | |
System.out.println("cache.put(1, 1)"); | |
cache.put(1, 1); | |
System.out.println("cache.put(2, 2)"); | |
cache.put(2, 2); | |
System.out.println("cache.get(1): " + cache.get(1)); | |
System.out.println("cache.put(3, 3)"); | |
cache.put(3, 3); | |
System.out.println("cache.get(2): " + cache.get(2)); | |
System.out.println("cache.put(4, 4)"); | |
cache.put(4, 4); | |
System.out.println("cache.get(1): " + cache.get(1)); | |
System.out.println("cache.get(3): " + cache.get(3)); | |
System.out.println("cache.get(4): " + cache.get(4)); | |
System.out.println(cache.cache); | |
} | |
private Map<Integer, Node> cache; | |
private Node head; | |
private Node tail; | |
private int capacity; | |
public LRUCache(int capacity) { | |
this.capacity = capacity; | |
// Here I am using ConcurrentHashMap just to be thread safe. | |
cache = new ConcurrentHashMap<>(); | |
head = new Node(0, 0); | |
tail = new Node(0, 0); | |
head.next = tail; | |
tail.pre = head; | |
head.pre = null; | |
tail.next = null; | |
} | |
public int get(int key) { | |
// if cache does not contains key return -1 | |
if (!cache.containsKey(key)) { | |
return -1; | |
} | |
// if it contains key get the linkedlist node | |
Node node = cache.get(key); | |
int result = node.value; | |
// delete the node from that linkedlist and add it to the head | |
deleteNode(node); | |
// adding node to head as it is recently used. | |
addToHead(node); | |
return result; | |
} | |
public void put(int key, int value) { | |
// check if it there in cache or not if it is in cache, | |
// add to the head of linkedlist | |
if (cache.get(key) != null) { | |
Node node = cache.get(key); | |
node.value = value; | |
deleteNode(node); | |
addToHead(node); | |
} else { // element is not in the cache so we have to add in cache and also to head of linkedlist | |
Node node = new Node(key, value); | |
cache.put(key, node); | |
// if cache has capacity add it | |
if (cache.size() <= capacity) { | |
addToHead(node); | |
} else { // cache does not have capacity remove last recently used element which is at tail | |
// here tail points to numm and so last element is tail.pre | |
cache.remove(tail.pre.key); | |
deleteNode(tail.pre); | |
addToHead(node); | |
} | |
} | |
} | |
public void deleteNode(Node node) { | |
node.pre.next = node.next; | |
node.next.pre = node.pre; | |
} | |
public void addToHead(Node node) { | |
node.next = head.next; | |
node.next.pre = node; | |
node.pre = head; | |
head.next = node; | |
} | |
// ------- Double Linked List Node -------- | |
private static class Node { | |
int key; | |
int value; | |
Node pre; | |
Node next; | |
public Node(int key, int value) { | |
this.key = key; | |
this.value = value; | |
} | |
@Override | |
public String toString() { | |
return " Node{" + | |
"k=" + key + | |
", v=" + value + | |
'}'; | |
} | |
} | |
} |
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