Triangular Number Java

PROGRAM TO CHECK IF A NUMBER IS TRIANGULAR

import java.io.*;

  

class GFG {

  

    // Returns true if num is triangular

    static boolean isTriangular(int num)

    {

        if (num < 0)

            return false;

      

        // Considering the equation 

        // n*(n+1)/2 = num

        // The equation is : 

        // a(n^2) + bn + c = 0";

        int c = (-2 * num);

        int b = 1, a = 1;

        int d = (b * b) - (4 * a * c);

      

        if (d < 0)

            return false;

      

        // Find roots of equation

        float root1 = ( -b + 

           (float)Math.sqrt(d)) / (2 * a);

             

        float root2 = ( -b - 

           (float)Math.sqrt(d)) / (2 * a);

      

        // checking if root1 is natural

        if (root1 > 0 && Math.floor(root1)

                                  == root1)

            return true;

      

        // checking if root2 is natural

        if (root2 > 0 && Math.floor(root2)

                                  == root2)

            return true;

      

        return false;

    }

      

    // Driver code

    public static void main (String[] args) {

        int num = 55;

        if (isTriangular(num))

            System.out.println("The number is"

                    + " a triangular number");

        else

            System.out.println ("The number "

              + "is NOT a triangular number");

    }

}

OUTPUT

 The number is a triangular number 

CREDITS: https://www.geeksforgeeks.org/triangular-numbers/