Java Program to Find Digital Roots of a Number by Using Recursion

Prerequisite: Recursion in Java

In the previous article, we have discussed about Java Program to Find First Uppercase Letter in a String by Using Recursion

In this program we are going to see how to find digital roots of a number by using Recursion in Java programming language.

Java Program to Find Digital Roots of a Number by Using Recursion

Let’s see an example to understand it clearly.

Assume there is a number say N = 1234
Then the sum of the digits of N = 1+2+3+4 = 10
If the sum of digits > 9 then again find the sum of digits.
Hence sum of digits of 10 is 1+0 = 1
So, the digital root of 1234 is 1

Now let’s see different ways to find digital roots of a number by using recursion.

By Using Static Input and Recursion
By Using User Input and Recursion

Method-1: Java Program to Find Digital Roots of a Number By Using Static Input and Recursion

Approach:

Declare and initialize an integer variable say ‘n’
Call a user defined method findDigitalRoot() method and pass ‘n’ as parameter to find the digital root of the given number .
Inside the user defined method we will find the sum of the digits of the number using a do while loop, if the sum of digits of the number exceeds 9 then we will call findDigitalRoot() method recursively. And finally we will return the sum value to the main() method.
Now the value of the user defined method findDigitalRoot() method is stored in an integer variable say ‘x’.
Print the value of digital root.

Program:

import java.util.*;
import java.io.*;
public class Main 
{
    public static void main(String[] args)
    {
        // declare and initialize an integer variable ‘n’
        int n = 7869;
        //call findDigitalRoot() method to find the digital root
        int x = findDigitalRoot(n);
        // print the result
        System.out.println("The digital root of the number "+n+" is: "+x);
    }
    
    //findDigitalRoot method
    static int findDigitalRoot(long n)
    {
        //storing the original integer value in a temporary variable
        long temp = n;
        long sum = 0;
        //to find sum of digits of a number
        do 
        {
            long remainder = temp%10;
            sum += remainder;
            temp = temp/10;
        } 
        while(temp!=0);
        //if the sum of digits of the number is greater than 9 then again find the sum of the digits using recursion
        if (sum > 9)
            return findDigitalRoot(sum);
        // if the sum of digits of the number is less than 10 then return the value
        return (int)sum;
    }
}

Output:

The digital root of the number 7869 is: 3

Method-2: Java Program to Find Digital Roots of a Number By Using User Input and Recursion

Approach:

Create a scanner class.
Declare an integer variable say ‘n’.
Prompt the user to enter a number.
Call a user defined method findDigitalRoot() method and pass ‘n’ as parameter to find the digital root of the given number .
Inside the user defined method we will find the sum of the digits of the number using a do while loop, if the sum of digits of the number exceeds 9 then we will call findDigitalRoot() method recursively. And finally we will return the sum value to the main() method.
Now the value of the user defined method findDigitalRoot() method is stored in an integer variable say ‘x’.
Print the value of digital root.

Program:

import java.util.*;
import java.io.*;
public class Main 
{
    public static void main(String[] args)
    {
        // create a scanner class
        Scanner s = new Scanner(System.in);
        System.out.println("Enter the number:");
        int n = s.nextInt();
        //call findDigitalRoot() method to find the digital root
        int x = findDigitalRoot(n);
        // print the result
        System.out.println("The digital root of the number "+n+" is: "+x);
    }
    
    //findDigitalRoot method
    static int findDigitalRoot(long n)
    {
        //storing the original integer value in a temporary variable
        long temp = n;
        long sum = 0;
        //to find sum of digits of a number
        do 
        {
            long remainder = temp%10;
            sum += remainder;
            temp = temp/10;
        } 
        while(temp!=0);
        //if the sum of digits of the number is greater than 9 then again find the sum of the digits using recursion
        if (sum > 9)
            return findDigitalRoot(sum);
        // if the sum of digits of the number is less than 10 then return the value
        return (int)sum;
    }
}

Output:

Enter the number:
1234
The digital root of the number 1234 is: 1

Guys who are serious about learning the concepts of the java programming language should practice this list of programs in java and get a good grip on it for better results in exams or interviews.

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