package Maths;

import java.util.ArrayList;
import java.util.Collections;

/**
 * n number theory, a vampire number (or true vampire number) is a composite natural number with an
 * even number of digits, that can be factored into two natural numbers each with half as many
 * digits as the original number and not both with trailing zeroes, where the two factors contain
 * precisely all the digits of the original number, in any order, counting multiplicity. The first
 * vampire number is 1260 = 21 ×ばつ 60. *
 *
 * <p>* link: https://en.wikipedia.org/wiki/Vampire_number *
 *
 * <p>
 */
public class VampireNumber {

 public static void main(String[] args) {

 test(10, 1000);
 }

 static void test(int startValue, int stopValue) {
 int countofRes = 1;
 StringBuilder res = new StringBuilder();

 for (int i = startValue; i <= stopValue; i++) {
 for (int j = i; j <= stopValue; j++) {
 // System.out.println(i+ " "+ j);
 if (isVampireNumber(i, j, true)) {
 countofRes++;
 res.append("" + countofRes + ": = ( " + i + "," + j + " = " + i * j + ")" + "\n");
 }
 }
 }
 System.out.println(res);
 }

 static boolean isVampireNumber(int a, int b, boolean noPseudoVamireNumbers) {

 // this is for pseudoVampireNumbers pseudovampire number need not be of length n/2 digits for
 // example
 // 126 = 6 x 21
 if (noPseudoVamireNumbers) {
 if (a * 10 <= b || b * 10 <= a) {
 return false;
 }
 }

 String mulDigits = splitIntoDigits(a * b, 0);
 String faktorDigits = splitIntoDigits(a, b);

 return mulDigits.equals(faktorDigits);
 }

 // methode to Split the numbers to Digits
 static String splitIntoDigits(int num, int num2) {

 StringBuilder res = new StringBuilder();

 ArrayList<Integer> digits = new ArrayList<>();
 while (num > 0) {
 digits.add(num % 10);
 num /= 10;
 }
 while (num2 > 0) {
 digits.add(num2 % 10);
 num2 /= 10;
 }
 Collections.sort(digits);
 for (int i : digits) {
 res.append(i);
 }

 return res.toString();
 }
}