LRU cache based on HashMap - Java Data Structure

Java examples for Data Structure:Cache

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Description

LRU cache based on HashMap

Demo Code


import java.util.HashMap;

class LRU {/*from   w  ww .  j  a v a  2s .  c o  m*/
  int capacity;
  HashMap<Integer, Node> map = new HashMap<Integer, Node>();
  Node head = null;
  Node end = null;

  public LRU(int capacity) {
    this.capacity = capacity;
  }

  public int get(int key) {
    if (map.containsKey(key)) {
      Node n = map.get(key);
      remove(n);
      setHead(n);
      return n.value;
    }

    return -1;
  }

  public void remove(Node n) {
    if (n.pre != null) {
      n.pre.next = n.next;
    } else {
      head = n.next;
    }

    if (n.next != null) {
      n.next.pre = n.pre;
    } else {
      end = n.pre;
    }

  }

  public void setHead(Node n) {
    n.next = head;
    n.pre = null;

    if (head != null)
      head.pre = n;

    head = n;

    if (end == null)
      end = head;
  }

  public void set(int key, int value) {
    if (map.containsKey(key)) {
      Node old = map.get(key);
      old.value = value;
      remove(old);
      setHead(old);
    } else {
      Node created = new Node(key, value);
      if (map.size() >= capacity) {
        map.remove(end.key);
        remove(end);
        setHead(created);

      } else {
        setHead(created);
      }

      map.put(key, created);
    }
  }

}

class Node {
  int key;
  int value;
  Node pre;
  Node next;

  public Node(int key, int value) {
    this.key = key;
    this.value = value;
  }
}

public class Main {
  public static void main(String args[]) {
    LRU lru = new LRU(4);

    lru.set(3, 3);
    lru.set(5, 5);
    lru.set(1, 1);
    lru.set(2, 2);
    lru.set(4, 4);
    lru.set(7, 7);

    System.out.println(lru.get(1));
    System.out.println(lru.get(2));
    System.out.println(lru.get(3));
    System.out.println(lru.get(4));
  }
}

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