Question

Java Language

Implement hash tables using open addressing and chaining

Test your implementation with sample values.

Answer 1

Please find the code below:

Custom Node class:

package different;

//custom Node class
public class Node<K,V> {
    //key
    K key;
    //value
    V value;
    //next node
    Node<K,V> next;

    //default constructor
    public Node(K key, V value){
        this.key = key;
        this.value = value;
    }
}

Custom Map class:

import java.util.ArrayList;


public class MyMap<K,V> {
    //list to store values
    ArrayList<Node<K,V>> myList;
    //capacity of list
    int capacity;
    //size of the list
    int size;
    //default constructor
    public MyMap(){
        myList = new ArrayList<>();
        //intial capacity
        capacity = 10;
        //intital size;
        size = 0;

        for(int i=0;i<capacity;i++){
            myList.add(null);
        }
    }
    //get size
    public int size(){
        return size;
    }
    //check if it's empty
    public boolean isEmpty(){
        return myList.isEmpty();
    }
    //find index
    int getIndex(K key){
        return key.hashCode() % capacity;
    }
    //add a key
    public void add(K key, V value){
        //get the first index for the key
        int index = getIndex(key);
        //get the node at index
        Node<K,V> chain_head = myList.get(index);

        //check if the key is present at that value
        while(chain_head!=null){
            if(chain_head.key.equals(key)){
                //update the value
                chain_head.value = value;
                return;
            }
            chain_head = chain_head.next;
        }

        //Else insert key into the cahin
        size++;
        chain_head = myList.get(index);
        Node<K,V> newNode = new Node<>(key, value);
        newNode.next = chain_head;

        myList.set(index,newNode);


        //If list is full by 80% then increase the capacity of the list

        if((size*1.0)/capacity >= 0.80){
            ArrayList<Node<K,V>> newList = myList;
            myList = new ArrayList<>();
            capacity = 2 * capacity;
            size = 0;
            for(int i=0;i<capacity;i++){
                myList.add(null);
            }

            for(Node<K,V> node : newList){
                while(node!=null){
                    add(node.key,node.value);
                    node = node.next;
                }
            }
        }
    }

    //get the value for given key
    public V get(K key){
        //find the fitst node in chain for given key
        int index = getIndex(key);
        Node<K,V> chain_head = myList.get(index);

        while(chain_head!=null){
            if(chain_head.key.equals(key)){
                return chain_head.value;
            }
            chain_head = chain_head.next;
        }

        return null;
    }

    //remove value for given key
    public V remove(K key){
        //find the fitst node in chain for given key
        int index = getIndex(key);
        Node<K,V> chain_head = myList.get(index);

        //serach for the given key node
        Node<K,V> prev = null;
        while(chain_head!=null){
            if(chain_head.key.equals(key)){
                break;
            }
            prev = chain_head;
            chain_head = chain_head.next;
        }

        if(chain_head==null){
            return null;
        }

        size--;

        if(prev!=null){
            prev.next = chain_head.next;
        }
        else{
            myList.set(index,chain_head.next);
        }

        return chain_head.value;
    }

    public static void main(String[] args) {
        MyMap<String,Integer> myMap = new MyMap<>();
        myMap.add("One",1);
        myMap.add("Two",2);
        myMap.add("Three",3);
        myMap.add("Four",4);
        System.out.println("Size: " + myMap.size());
        System.out.println("Removed Value: " + myMap.remove("Three"));
        System.out.println("Size: " + myMap.size());
        System.out.println("Is Empty?: " + myMap.isEmpty());
        System.out.println("Value with Key \"One\": " + myMap.get("One"));
    }

}

Output:

"C:\Program Files\Javaljakl. 8.0-151\bin\java" Size: 4 Removed Value: 3 11 | size : 3 Is Empty?: false Value with Key "One" 1