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Java program to check whether given number is Kaprekar number or not

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mahmoud2506
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2022-05-06
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Given an integer number and we have to check whether it is a Kaprekar number or not using Java program.

What is Kaprekar Number?

A Kaprekar number is a number in which the sum of digits in its square is the number itself.

Example:

    
    9*2= 81 (Square of 9)
    8+1 = 9(Sum of digits in square)

 

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mahmoud2506
2022-05-06
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Program to check given number Kaprekar Number or not in Java

public class KaprekarNumbers 
{
	public static void main(String[] args)
	{
		int ctr = 0;
		int base = (args.length > 0) ? Integer.parseInt(args[0]) : 10;

		for(long n = 1; n <= 1000; n++)
		{
			String St = Long.toString(n * n, base);

			for(int j = 0; j < St.length() / 2 + 1; j++)
			{
				String[] S = split_num(St, j);

				long N1 = Long.parseLong(S[0], base);
				long N2 = Long.parseLong(S[1], base);

				if(N2 == 0) break;

				if(N1 + N2 == n)
				{
					System.out.println(Long.toString(n, base) +"\t" + St + "\t  " + S[0] + " + " + S[1]);
					ctr++;
					break;
				}
			}
		}
		System.out.println(ctr + " Kaprekar numbers.");
		}

		private static String[] split_num(String str, int idx)
		{
		String[] A1 = new String[2];
		A1[0] = str.substring(0, idx);

		if(A1[0].equals("")) A1[0] = "0"; 
		A1[1] = str.substring(idx);
		return A1;
	}	
}

Output

First run:
Kaprekar number between 1 to 1000.

1	1	  0 + 1
9	81	  8 + 1
45	2025	  20 + 25
55	3025	  30 + 25
99	9801	  98 + 01
297	88209	  88 + 209
703	494209	  494 + 209
999	998001	  998 + 001
8 Kaprekar numbers.

Second run:
Kaprekar number between 1 to 100.

1	1	  0 + 1
9	81	  8 + 1
45	2025	  20 + 25
55	3025	  30 + 25
99	9801	  98 + 01
5 Kaprekar numbers.

 

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