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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.lang.*;
  5. import java.io.*;
  6.  
  7. /* Name of the class has to be "Main" only if the class is public. */
  8. class Ideone
  9. {
  10. 	 /**
  11.          *
  12.          * @param numberOfDigits {int}
  13.          * @return ArrayList of Integer
  14.          */
  15.         public ArrayList<Integer> vdf(int numberOfDigits) {
  16.  
  17.             if ((numberOfDigits % 2) == 1) { 
  18.                 //or throw Exception of unrecognised format/variable?
  19.                 System.out.println("cant operate on odd argument");
  20.                 return new ArrayList<>();
  21.             }
  22.             long maxRange = 9;
  23.  
  24.             for (int i = 1; i < numberOfDigits; i++) {
  25.                 maxRange *= 10;
  26.                 maxRange += 9;
  27.             }//numberOfDigits==4 then maxRange==9999, nOD==5 then maxRange==99999,..
  28.  
  29.             long minRange = 1;
  30.  
  31.             for (int i = 1; i < numberOfDigits; i++) {
  32.                 minRange *= 10;
  33.             }//nOD==4 then minRange==1000, nOD==5 then minRange==10000, ..
  34.  
  35.             ArrayList<Integer> ret = new ArrayList<>();
  36.             for (long i = minRange; i < maxRange; i++) {
  37.  
  38.                 long a = i;
  39.  
  40.                 long[] b = new long[numberOfDigits];
  41.  
  42.                 for (int j = numberOfDigits-1; j >= 0 ; j--) {
  43.                     long c = a % 10;
  44.                     a = a / 10;
  45.                     b[j] = c;
  46.                 }
  47.  
  48.                 int x = 0;
  49.                 int y = 0;
  50.                 ArrayList<long[]> list = permutations(b);
  51.                 b = null; //dont need now
  52.  
  53.                 for(long[] s : list) {
  54.                     for (int j = 0; j < numberOfDigits/2; j++) {
  55.                         x += s[(numberOfDigits/2)-j-1] * Math.pow(10, j);
  56.                         y += s[numberOfDigits-j-1] * Math.pow(10, j);
  57.                     }
  58.                     StringBuilder builder = new StringBuilder();
  59.                     for (long t : s) {
  60.                         builder.append(t);
  61.                     }
  62.                     String v = builder.toString();
  63.  
  64.                     if ((v.charAt((v.length()/2)-1) != '0'||
  65.                         v.charAt(v.length()-1) != '0') &&
  66.                         x * y == i) {
  67.                         ret.add(x);
  68.                         ret.add(y);
  69.                         System.out.println(x*y+"  "+x+" "+y);
  70.                         break;
  71.                     }
  72.                     x = y = 0;
  73.                 }
  74.             }
  75.             System.out.printf("%d vampire numbers found\n", ret.size()/2);
  76.             return ret;
  77.         }
  78.  
  79.         /**
  80.          * 
  81.          *@return vdf(4)
  82.          */
  83.         public ArrayList<Integer> vdf() {
  84.             return vdf(4);//without trailing zeros
  85.         }
  86.  
  87.         /* permutation code copied from  
  88.          * johk95
  89.          * http://stackoverflow.com/a/20906510
  90.          */
  91.         private static ArrayList<long[]> permutations(long[] lol) {
  92.             ArrayList<long[]> ret = new ArrayList<>();
  93.             permutation(lol, 0, ret);
  94.             return ret;
  95.         }
  96.  
  97.         private static void permutation(long[] arr, int pos, ArrayList<long[]> list){
  98.             if(arr.length - pos == 1)
  99.                 list.add(arr.clone());
  100.             else
  101.                 for(int i = pos; i < arr.length; i++){
  102.                     swap(arr, pos, i);
  103.                     permutation(arr, pos+1, list);
  104.                     swap(arr, pos, i);
  105.                 }
  106.         }
  107.  
  108.         private static void swap(long[] arr, int pos1, int pos2){
  109.             long h = arr[pos1];
  110.             arr[pos1] = arr[pos2];
  111.             arr[pos2] = h;
  112.         }
  113.  
  114.         public static void main(String[] args) {
  115.             Ideone a = new Ideone();
  116.             try{
  117.                 a.vdf(4);
  118.             }catch (java.lang.OutOfMemoryError e){
  119.                 System.err.println(e.getMessage());
  120.             }
  121.         }
  122.  
  123. }
Success #stdin #stdout 0.35s 320576KB
comments (?)
stdin 
Standard input is empty
stdout 
1260  21 60
1395  15 93
1435  41 35
1530  51 30
1827  87 21
2187  27 81
6880  86 80
7 vampire numbers found
https://ideone.com/3rHhep
vampire numbers generator @nanomader
language:
Java (HotSpot 12)
created:
10 years ago
visibility:
public

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