Magic Numbers in Java

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The number whose sum if calculated to single digit turns out to be 1 then the number is called Magic number.

Example 1 :- 1234

1+2+3+4 = 10

1+0 = 1

Since we got the sum to be 1 hence 1234 is a Magic number.

Example 2 :- 7111

7+1+1+1 = 10

1+0 = 1

Sum turned out to be 1 hence 7111 is a magic number.

Example 3 :- 12345

1+2+3+4+5 = 15

1+5 = 6

Sum is 6 so 12345 is not a magic number.

Let us see how we can implement the logic for Magic number in Java. We will use 2 ways to code the logic. First method uses 2 nested loops. The second method uses single loop.

Method 1 (Easier to understand) :-

public class Tech4Humans {

	public static void main(String[] args) {
		int num = 7111;
		boolean result = checkMagicNumber(num);
		if (result) {
			System.out.println(num + " is a magic number");
		} else {
			System.out.println(num + " is not a magic number");
		}
	}

	static boolean checkMagicNumber(int num) {
		int sum, tempNum = num;
		do {
			sum = 0;
			while (tempNum > 0) {
				sum = sum + (tempNum % 10);
				tempNum = tempNum / 10;
			}
			tempNum = sum;
		} while (sum > 9);
		if (sum == 1) {
			return true;
		}
		return false;
	}
}

Output

7111 is a magic number

Method 2 (Cleaner Code and Single loop) :-

public class Tech4Humans {

	public static void main(String[] args) {
		int num = 1234;
		boolean result = checkMagicNumber(num);
		if (result) {
			System.out.println(num + " is a magic number");
		} else {
			System.out.println(num + " is not a magic number");
		}
	}

	static boolean checkMagicNumber(int num) {
		int sum = 0, tempNum = num;
		while (sum > 9 || tempNum > 0) {
			if (tempNum == 0) {
				tempNum = sum;
				sum = 0;
			}
			sum = sum + (tempNum % 10);
			tempNum = tempNum / 10;
		}
		if (sum == 1) {
			return true;
		}
		return false;
	}

}

Output

1234 is a magic number

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