Change project structure to a Maven Java project + Refactor (#2816)

src/main/java/com/thealgorithms/maths/VampireNumber.java

@@ -0,0 +1,80 @@
+package com.thealgorithms.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 × 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();
+    }
+}