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@deepshah22
Last active Sep 5, 2020
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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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