programming-examples/java/Data_Structures/Java Program to Implement Hash Tables Chaining with Binary Trees.java

/*This is a Java Program to implement hash tables chaining with Binary Trees. A hash table (also hash map) is a data structure used to implement an associative array, a structure that can map keys to values. A hash table uses a hash function to compute an index into an array of buckets or slots, from which the correct value can be found. In order to prevent collision, hash tables are chained with another data structure ( Binary Trees in this case ).*/

/*
 *    Java Program to Implement Hash Tables Chaining with Binary Trees
 */

import java.util.Scanner;

/* Node for Binary Tree */
class BTNode
{
    BTNode left, right;
    int data;

    /* Constructor */
    public BTNode(int x)
    {
        data = x;
        left = null;
        right = null;
    }
}

/* Class HashTableChainingBinaryTree */
class HashTableChainingBinaryTree
{
    private BTNode[] table;
    private int size ;

    /* Constructor */
    public HashTableChainingBinaryTree(int tableSize)
    {
        table = new BTNode[ nextPrime(tableSize) ];
        size = 0;
    }
    /* Function to check if hash table is empty */
    public boolean isEmpty()
    {
        return size == 0;
    }
    /* Function to clear hash table */
    public void makeEmpty()
    {
        int l = table.length;
        table = new BTNode[l];
        size = 0;
    }
    /* Function to get size */
    public int getSize()
    {
        return size;
    }
    /* Function to insert an element */
    public void insert(int val)
    {
        size++;
        int pos = myhash(val);
        BTNode root = table[pos];
        root = insert(root, val);
        table[pos] = root;
    }
    /* Function to insert data */
    private BTNode insert(BTNode node, int data)
    {
        if (node == null)
            node = new BTNode(data);
        else
            {
                if (data <= node.data)
                    node.left = insert(node.left, data);
                else
                    node.right = insert(node.right, data);
            }
        return node;
    }
    /* Function to remove an element */
    public void remove(int val)
    {
        int pos = myhash(val);
        BTNode root = table[pos];
        try
            {
                root = delete(root, val);
                size--;
            }
        catch (Exception e)
            {
                System.out.println("\nElement not present\n");
            }
        table[pos] = root;
    }
    /* Function to remove an element */
    private BTNode delete(BTNode root, int k)
    {
        BTNode p, p2, n;
        if (root.data == k)
            {
                BTNode lt, rt;
                lt = root.left;
                rt = root.right;
                if (lt == null && rt == null)
                    return null;
                else if (lt == null)
                    {
                        p = rt;
                        return p;
                    }
                else if (rt == null)
                    {
                        p = lt;
                        return p;
                    }
                else
                    {
                        p2 = rt;
                        p = rt;
                        while (p.left != null)
                            p = p.left;
                        p.left = lt;
                        return p2;
                    }
            }
        if (k < root.data)
            {
                n = delete(root.left, k);
                root.left = n;
            }
        else
            {
                n = delete(root.right, k);
                root.right = n;
            }
        return root;
    }
    /* Function myhash */
    private int myhash(Integer x )
    {
        int hashVal = x.hashCode( );
        hashVal %= table.length;
        if (hashVal < 0)
            hashVal += table.length;
        return hashVal;
    }
    /* Function to generate next prime number >= n */
    private static int nextPrime( int n )
    {
        if (n % 2 == 0)
            n++;
        for ( ; !isPrime( n ); n += 2);
        return n;
    }
    /* Function to check if given number is prime */
    private static boolean isPrime( int n )
    {
        if (n == 2 || n == 3)
            return true;
        if (n == 1 || n % 2 == 0)
            return false;
        for (int i = 3; i * i <= n; i += 2)
            if (n % i == 0)
                return false;
        return true;
    }
    /* printing hash table */
    public void printHashTable ()
    {
        System.out.println();
        for (int i = 0; i < table.length; i++)
            {
                System.out.print ("Bucket " + i + ":  ");
                inorder(table[i]);
                System.out.println();
            }
    }
    /* inorder traversal */
    private void inorder(BTNode r)
    {
        if (r != null)
            {
                inorder(r.left);
                System.out.print(r.data +" ");
                inorder(r.right);
            }
    }
}

/* Class HashTableChainingBinaryTreeTest */
public class HashTableChainingBinaryTreeTest
{
    public static void main(String[] args)
    {
        Scanner scan = new Scanner(System.in);
        System.out.println("Hash Table Test\n\n");
        System.out.println("Enter size");
        /* Make object of HashTableChainingBinaryTree  */
        HashTableChainingBinaryTree htcbt = new HashTableChainingBinaryTree(scan.nextInt() );
        char ch;
        /*  Perform HashTableChainingBinaryTree operations  */
        do
            {
                System.out.println("\nHash Table Operations\n");
                System.out.println("1. insert ");
                System.out.println("2. remove");
                System.out.println("3. clear");
                System.out.println("4. size");
                System.out.println("5. check empty");
                int choice = scan.nextInt();
                switch (choice)
                    {
                    case 1 :
                        System.out.println("Enter integer element to insert");
                        htcbt.insert( scan.nextInt() );
                        break;
                    case 2 :
                        System.out.println("Enter integer element to delete");
                        htcbt.remove( scan.nextInt() );
                        break;
                    case 3 :
                        htcbt.makeEmpty();
                        System.out.println("Hash Table Cleared\n");
                        break;
                    case 4 :
                        System.out.println("Size = "+ htcbt.getSize() );
                        break;
                    case 5 :
                        System.out.println("Empty status = "+ htcbt.isEmpty() );
                        break;
                    default :
                        System.out.println("Wrong Entry \n ");
                        break;
                    }
                /* Display hash table */
                htcbt.printHashTable();
                System.out.println("\nDo you want to continue (Type y or n) \n");
                ch = scan.next().charAt(0);
            }
        while (ch == 'Y'|| ch == 'y');
    }
}

/*

Enter size
5

Hash Table Operations

1. insert
2. remove
3. clear
4. size
5. check empty
1
Enter integer element to insert
56

Bucket 0:
Bucket 1:  56
Bucket 2:
Bucket 3:
Bucket 4:

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. clear
4. size
5. check empty
1
Enter integer element to insert
78

Bucket 0:
Bucket 1:  56
Bucket 2:
Bucket 3:  78
Bucket 4:

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. clear
4. size
5. check empty
1
Enter integer element to insert
23

Bucket 0:
Bucket 1:  56
Bucket 2:
Bucket 3:  23 78
Bucket 4:

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. clear
4. size
5. check empty
1
Enter integer element to insert
44

Bucket 0:
Bucket 1:  56
Bucket 2:
Bucket 3:  23 78
Bucket 4:  44

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. clear
4. size
5. check empty
1
Enter integer element to insert
60

Bucket 0:  60
Bucket 1:  56
Bucket 2:
Bucket 3:  23 78
Bucket 4:  44

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. clear
4. size
5. check empty
97
Wrong Entry


Bucket 0:  60
Bucket 1:  56
Bucket 2:
Bucket 3:  23 78
Bucket 4:  44

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. clear
4. size
5. check empty
1
Enter integer element to insert
97

Bucket 0:  60
Bucket 1:  56
Bucket 2:  97
Bucket 3:  23 78
Bucket 4:  44

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. clear
4. size
5. check empty
1
Enter integer element to insert
7

Bucket 0:  60
Bucket 1:  56
Bucket 2:  7 97
Bucket 3:  23 78
Bucket 4:  44

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. clear
4. size
5. check empty
2
Enter integer element to delete
78

Bucket 0:  60
Bucket 1:  56
Bucket 2:  7 97
Bucket 3:  23
Bucket 4:  44

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. clear
4. size
5. check empty
4
Size = 6

Bucket 0:  60
Bucket 1:  56
Bucket 2:  7 97
Bucket 3:  23
Bucket 4:  44

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. clear
4. size
5. check empty
3
Hash Table Cleared


Bucket 0:
Bucket 1:
Bucket 2:
Bucket 3:
Bucket 4:

Do you want to continue (Type y or n)

y

Hash Table Operations

1. insert
2. remove
3. clear
4. size
5. check empty
5
Empty status = true

Bucket 0:
Bucket 1:
Bucket 2:
Bucket 3:
Bucket 4:

Do you want to continue (Type y or n)

n