79 lines
2.1 KiB
Java
79 lines
2.1 KiB
Java
package Maths;
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import java.util.ArrayList;
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import java.util.Collections;
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/**
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* n number theory, a vampire number (or true vampire number) is a composite natural number with an
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* even number of digits, that can be factored into two natural numbers each with half as many
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* digits as the original number and not both with trailing zeroes, where the two factors contain
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* precisely all the digits of the original number, in any order, counting multiplicity. The first
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* vampire number is 1260 = 21 × 60. *
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*
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* <p>* link: https://en.wikipedia.org/wiki/Vampire_number *
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*
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* <p>
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*/
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public class VampireNumber {
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public static void main(String[] args) {
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test(10, 1000);
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}
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static void test(int startValue, int stopValue) {
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int countofRes = 1;
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StringBuilder res = new StringBuilder();
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for (int i = startValue; i <= stopValue; i++) {
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for (int j = i; j <= stopValue; j++) {
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// System.out.println(i+ " "+ j);
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if (isVampireNumber(i, j, true)) {
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countofRes++;
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res.append("" + countofRes + ": = ( " + i + "," + j + " = " + i * j + ")" + "\n");
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}
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}
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}
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System.out.println(res);
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}
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static boolean isVampireNumber(int a, int b, boolean noPseudoVamireNumbers) {
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// this is for pseudoVampireNumbers pseudovampire number need not be of length n/2 digits for
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// example
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// 126 = 6 x 21
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if (noPseudoVamireNumbers) {
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if (a * 10 <= b || b * 10 <= a) {
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return false;
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}
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}
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String mulDigits = splitIntoDigits(a * b, 0);
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String faktorDigits = splitIntoDigits(a, b);
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return mulDigits.equals(faktorDigits);
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}
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// methode to Split the numbers to Digits
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static String splitIntoDigits(int num, int num2) {
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StringBuilder res = new StringBuilder();
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ArrayList<Integer> digits = new ArrayList<>();
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while (num > 0) {
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digits.add(num % 10);
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num /= 10;
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}
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while (num2 > 0) {
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digits.add(num2 % 10);
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num2 /= 10;
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}
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Collections.sort(digits);
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for (int i : digits) {
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res.append(i);
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}
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return res.toString();
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}
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}
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