Task: Vampire number



C#: using System;

namespace RosettaVampireNumber
{
    class Program
    {
        static void Main(string[] args)
        {
            int i, j, n;
            ulong x;
            var f = new ulong[16];
            var bigs = new ulong[] { 16758243290880UL, 24959017348650UL, 14593825548650UL, 0 };
            ulong[] tens = new ulong[20];
            tens[0] = 1;
            for (i = 1; i < 20; i++)
                tens[i] = tens[i - 1] * 10;
            
            for (x = 1, n = 0; n < 25; x++)
            {
                if ((j = fangs(x, f, tens)) == 0) continue;
                Console.Write(++n + ": ");
                show_fangs(x, f, j);
            }

            Console.WriteLine();
            for (i = 0; bigs[i] > 0 ; i++)
            {
                if ((j = fangs(bigs[i], f, tens)) > 0)
                    show_fangs(bigs[i], f, j);
                else
                    Console.WriteLine(bigs[i] + " is not vampiric.");
            }
            Console.ReadLine();
        }

        private static void show_fangs(ulong x, ulong[] f, int cnt)
        {
            Console.Write(x); 
            int i;
            for (i = 0; i < cnt; i++)
                Console.Write(" = " + f[i] + " * " + (x / f[i]));
            Console.WriteLine();
        }

        private static int fangs(ulong x, ulong[] f, ulong[] tens)
        {
            int n = 0;
            int nd = ndigits(x);
            if ((nd & 1) > 0) return 0;
            nd /= 2;

            ulong lo, hi;
            lo = Math.Max(tens[nd - 1], (x + tens[nd] - 2) / (tens[nd] - 1));
            hi = Math.Min(x / lo, (ulong) Math.Sqrt(x));

            ulong a, b, t = dtally(x);
            for (a = lo; a <= hi; a++)
            {
                b = x / a;
                if (a * b == x && ((a % 10) > 0 || (b % 10) > 0) && t == dtally(a) + dtally(b))
                    f[n++] = a;
            }

            return n;
        }

        private static ulong dtally(ulong x)
        {
            ulong t = 0;
            while (x > 0)
            {
                t += 1UL << (int)((x % 10) * 6);
                x /= 10;
            }

            return t;
        }

        private static int ndigits(ulong x)
        {
            int n = 0;
            while (x > 0)
            {
                n++;
                x /= 10;
            }
            return n;
        }
    }
}



Java: import java.util.Arrays;
import java.util.HashSet;

public class VampireNumbers{
    private static int numDigits(long num){
        return Long.toString(Math.abs(num)).length();
    }

    private static boolean fangCheck(long orig, long fang1, long fang2){
        if(Long.toString(fang1).endsWith("0") && Long.toString(fang2).endsWith("0")) return false;

        int origLen = numDigits(orig);
        if(numDigits(fang1) != origLen / 2 || numDigits(fang2) != origLen / 2) return false;

        byte[] origBytes = Long.toString(orig).getBytes();
        byte[] fangBytes = (Long.toString(fang1) + Long.toString(fang2)).getBytes();
        Arrays.sort(origBytes);
        Arrays.sort(fangBytes);
        return Arrays.equals(origBytes, fangBytes);
    }

    public static void main(String[] args){
        HashSet<Long> vamps = new HashSet<Long>();
        for(long i = 10; vamps.size() <= 25; i++ ){
            if((numDigits(i) % 2) != 0) {i = i * 10 - 1; continue;}
            for(long fang1 = 2; fang1 <= Math.sqrt(i) + 1; fang1++){
                if(i % fang1 == 0){
                    long fang2 = i / fang1;
                    if(fangCheck(i, fang1, fang2) && fang1 <= fang2){
                        vamps.add(i);
                        System.out.println(i + ": [" + fang1 + ", " + fang2 +"]");
                    }
                }
            }
        }
        Long[] nums = {16758243290880L, 24959017348650L, 14593825548650L};
        for(Long i : nums){
            for(long fang1 = 2; fang1 <= Math.sqrt(i) + 1; fang1++){
                if(i % fang1 == 0){
                    long fang2 = i / fang1;
                    if(fangCheck(i, fang1, fang2) && fang1 <= fang2){
                        System.out.println(i + ": [" + fang1 + ", " + fang2 +"]");
                    }
                }
            }
        }
    }
}