implementingHashmap.java

package Hashing;
import java.util.*;
public class implementingHashmap {
    static class HashMap<K,V>{
        private class Node{
            K key;
            V value;
            public Node (K key, V value){//generic
                this.key=key;
                this.value=value;
            }
        }

            private int n;
            private LinkedList<Node> buckets[];
            private int N;
            @SuppressWarnings("unchecked")
            public HashMap(){
                this.N=4;
                this.buckets=new LinkedList[4];
                for(int i=0;i<4;i++){
                    this.buckets[i]=new LinkedList<>();
                }
            }
            private int hashFunc(K key){
                int hc=key.hashCode();
                return Math.abs(hc)%N;
            }
            private int serachInLL(K key, int bi){
                LinkedList<Node> ll = buckets[bi];
                int di=0;
                for(int i=0; i<ll.size();i++){
                    Node node =ll.get(i);
                    if(node.key==key){
                        return di;
                    }
                    di++;
                }
                return -1;
            }
            @SuppressWarnings("unchecked")
            private void rehash(){
                ArrayList<Node> oldBuck[]=buckets;
                buckets=new LinkedList[N*2];
                N=2*N;
                for(int i=0;i<buckets.length;i++){
                    buckets[i]=new LinkedList<>();
                }
                //node->add in buckets
                for(int i=0;i<oldBuck.length;i++){
                    LinkedList<Node> ll=oldBuck[i];
                    for(int j=0;j<ll.size();j++){
                        Node node=ll.remove();
                        Put(node.key, node.value);
                    }
                }
            }


            public void Put(K key , V value){
                int bi=hashFunc(key);
                int di=serachInLL(key, bi);

                if(di!=-1){
                    Node node=buckets[bi].get(di);
                    node.value=value;

                }else{
                    buckets[bi].add(new Node(key, value));
                    n++;
                }
                double lambda=(double)n/N;
                if(lambda>2.0){
                    rehash();
                }
                }
                public boolean containsKey(K key){
                    int bi=hashFunc(key);
                    int di=serachInLL(key, bi);
                    if(di!=-1){
                        return true;
                    }else{
                        return false;
                    }
                }
                public V get(K key){
                    int bi=hashFunc(key);
                    int di=serachInLL(key, bi);
    
                    if(di!=-1){
                        Node node=buckets[bi].get(di);
                        return node.value;
    
                    }else{
                        return null;
                    }
                    
                }
                public V remove(K key){
                    int bi=hashFunc(key);
                    int di=serachInLL(key, bi);
    
                    if(di!=-1){
                        Node node=buckets[bi].remove(di);
                        n--;
                        return node.value;
    
                    }else{
                        return null;
                    }
                }
                public ArrayList<K> keyset(){
                    ArrayList<K> keys=new ArrayList<>();
                    for (int i=0;i<buckets.length;i++) {
                        LinkedList<Node> ll=buckets[i];
                        for (Node node  : ll) {
                            keys.add(node.key);
                        }
                    }
                    return keys;
                }
                public boolean isEmpty(){return n==0;}
                

        public static void main(String[] args) {
            HashMap<String,Integer>hm=new HashMap<>();
            hm.Put("India", 100);
            hm.Put("Chaina", 150);
            ArrayList<String> keys=hm.keyset();
            for (String key  : keys) {
                System.out.println(key);
            }
        }
    }
}