2016 Update

Task/Vampire-number/00DESCRIPTION

@@ -2,12 +2,22 @@ A [[wp:Vampire_number|vampire number]] is a natural number with an even number o
 * they each contain half the number of the digits of the original number
 * together they consist of exactly the same digits as the original number
 * at most one of them has a trailing zero
-An example of a Vampire number and its fangs: <code>1260 : (21, 60)</code>
-;<nowiki>Task description:</nowiki>
+
+<br>
+An example of a Vampire number and its fangs: <code> 1260 : (21, 60) </code>
+
+
+;Task:
 # Print the first 25 Vampire numbers and their fangs.
-# Check if the following numbers are Vampire numbers and, if  so, print them and their fangs: <code>16758243290880, 24959017348650, 14593825548650</code>
-Note that a Vampire number can have more than 1 pair of fangs.
-;<nowiki>See also:</nowiki>
+# Check if the following numbers are Vampire numbers and, if  so, print them and their fangs:
+<big><code> 16758243290880,  24959017348650,  14593825548650 </code></big>
+
+<br>
+Note that a Vampire number can have more than one pair of fangs.
+
+
+;See also:
 * [http://www.numberphile.com/videos/vampire_numbers.html numberphile.com].
 * [http://users.cybercity.dk/~dsl522332/math/vampires/ Vampire search algorithm]
 * [[oeis:A014575|Vampire numbers on OEIS]]
+<br><br>

Task/Vampire-number/Elixir/vampire-number.elixir

@@ -0,0 +1,42 @@
+defmodule Vampire do
+  def factor_pairs(n) do
+    first = trunc(n / :math.pow(10, div(char_len(n), 2)))
+    last  = :math.sqrt(n) |> round
+    for i <- first .. last, rem(n, i) == 0, do: {i, div(n, i)}
+  end
+
+  def vampire_factors(n) do
+    if rem(char_len(n), 2) == 1 do
+      []
+    else
+      half = div(length(to_char_list(n)), 2)
+      sorted = Enum.sort(String.codepoints("#{n}"))
+      Enum.filter(factor_pairs(n), fn {a, b} ->
+        char_len(a) == half && char_len(b) == half &&
+        Enum.count([a, b], fn x -> rem(x, 10) == 0 end) != 2 &&
+        Enum.sort(String.codepoints("#{a}#{b}")) == sorted
+      end)
+    end
+  end
+
+  defp char_len(n), do: length(to_char_list(n))
+
+  def task do
+    Enum.reduce_while(Stream.iterate(1, &(&1+1)), 1, fn n, acc ->
+      case vampire_factors(n) do
+        [] -> {:cont, acc}
+        vf -> IO.puts "#{n}:\t#{inspect vf}"
+              if acc < 25, do: {:cont, acc+1}, else: {:halt, acc+1}
+      end
+    end)
+    IO.puts ""
+    Enum.each([16758243290880, 24959017348650, 14593825548650], fn n ->
+      case vampire_factors(n) do
+        [] -> IO.puts "#{n} is not a vampire number!"
+        vf -> IO.puts "#{n}:\t#{inspect vf}"
+      end
+    end)
+  end
+end
+
+Vampire.task

Task/Vampire-number/Perl-6/vampire-number.pl6

@@ -1,8 +1,19 @@
-my @vampires := gather for 1 .. * -> $start, $end {
-    map {
-        my @fangs = is_vampire($_);
-        take "$_: { @fangs.join(', ') }" if @fangs.elems
-    }, 10 ** $start .. 10 ** $end
+sub is_vampire (Int $num) {
+    my $digits = $num.comb.sort;
+    my @fangs;
+    for vfactors($num) -> $this {
+        my $that = $num div $this;
+        @fangs.push("$this x $that") if
+            !($this %% 10 && $that %% 10) and
+            ($this ~ $that).comb.sort eq $digits;
+    }
+    return @fangs;
+}
+
+constant @vampires = gather for 1 .. * -> $n {
+    next if $n.log(10).floor %% 2;
+    my @fangs = is_vampire($n);
+    take "$n: { @fangs.join(', ') }" if @fangs.elems;
 }
 
 say "\nFirst 25 Vampire Numbers:\n";
@@ -21,18 +32,6 @@ for 16758243290880, 24959017348650, 14593825548650 {
     }
 }
 
-sub is_vampire (Int $num) {
-    my $digits = $num.comb.sort;
-    my @fangs;
-    for vfactors($num) -> $this {
-        my $that = $num div $this;
-        @fangs.push("$this x $that") if
-            !($this %% 10 && $that %% 10) and
-            ($this ~ $that).comb.sort eq $digits;
-    }
-    return @fangs;
-}
-
 sub vfactors (Int $n) {
    map { $_ if $n %% $_ }, 10**$n.sqrt.log(10).floor .. $n.sqrt.ceiling;
 }