Java program to check if a number is a ugly number or not

Java program to check if a number is a ugly number or not:

In this post, we will learn how to check if a number is a ugly number or not using Java. The program will ask the user to enter a number, it will read that number and check if it is ugly or not.

Before we move to the program, let’s understand what are ugly numbers i.e. the definition of ugly numbers.

Definition of ugly number:

A number is called a ugly number if its prime factors are 2, 3 and 5. For example, 15 is ugly number because its factors are 1 * 3 * 5. 1 is also considered as ugly number.

Let’s write a Java program that checks if a given number is ugly number or not.

Java program to check if a number is ugly or not:

The below program takes one number as input from the user and checks if that number is ugly or not:

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        boolean isUgly = true;
        Scanner sc = new Scanner(System.in);

        System.out.println("Enter a number: ");
        int no = sc.nextInt();

        while (no != 1) {
            if (no % 5 == 0) {
                no = no / 5;
            } else if (no % 3 == 0) {
                no = no / 3;
            } else if (no % 2 == 0) {
                no = no / 2;
            } else {
                isUgly = false;
                break;
            }
        }

        if (isUgly) {
            System.out.println("It is an ugly number");
        } else {
            System.out.println("It is not an ugly number");
        }

    }
}

Here,

isUgly is a boolean. It is initialized as true. It is assigned false if the given number is not ugly.
The Scanner variable sc is used to read the user input number
The while loop runs until the value of the number is 1. Inside this loop, it divides the number by 5, 3 or 2. If it can’t divide it by any of these numbers, it assigns false to isUgly and exits from the loop.
The last if-else block is checking the value of isUgly and based on the value, it prints a message.

If you run this program, it will print output as like below:

Enter a number: 
100
It is an ugly number

Print all ugly numbers from 1 to 100:

Let’s write a Java program to print all ugly numbers from 1 to 100. We can move the above code that checks if a number is ugly or not to a different method and use that method for all numbers from 1 to 100 using a loop.

public class Main {

    private static boolean isUgly(int no) {
        while (no != 1) {
            if (no % 5 == 0) {
                no = no / 5;
            } else if (no % 3 == 0) {
                no = no / 3;
            } else if (no % 2 == 0) {
                no = no / 2;
            } else {
                return false;
            }
        }
        return true;
    }

    public static void main(String[] args) {
        for (int i = 1; i <= 100; i++) {
            if (isUgly(i)) {
                System.out.println(i);
            }
        }
    }
}

Here,

isUgly method checks if a number is ugly or not. It takes one integer value and returns one boolean. true if the integer is ugly, false otherwise.
It uses a while loop in a similar way as we did for the previous program.
Inside main, we are using a for loop that runs from 1 to 100 that checks and prints all ugly numbers.

If you run this program, it will print all ugly numbers from 1 to 100:

Or, you can use System.out.print(i + ” ”); to print these in one line:

1 2 3 4 5 6 8 9 10 12 15 16 18 20 24 25 27 30 32 36 40 45 48 50 54 60 64 72 75 80 81 90 96 100

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Java program to check if a number is a ugly number or not