# ETOOBUSY ðŸš€ minimal blogging for the impatient

# Disarium Numbers: brute force won't cut it

**TL;DR**

A brute force attack to the Disarium Numbers challenge did not work for me.

My routine for The Weekly Challenge is to attack the first one in
*Raku then Perl* order and the second one the other way around.

My approach is also to use brute force whenever possible, even though I
*feel* that there might be more to it. Thereâ€™s an interesting internal
tension between the more *scientific* part that would like to know more,
and the more *engineering* part that just wants to get the job done with
as few resources as possible (I mean, my resources).

So this time I went for the usual way and wrote a very basic brute-force solution in Raku:

```
#!/usr/bin/env raku
use v6;
sub MAIN (Int:D $n where * > 0 = 19) {
my $candidate = 0;
my $i = 0;
while $i < $n {
if is-disarium($candidate) {
"\%0{$n.chars()}d. %d".sprintf(++$i, $candidate).put;
}
++$candidate;
}
}
sub is-disarium (Int:D $n where $n >= 0) {
$n == $n.comb.kv.map(-> $x, $y { $y ** ($x + 1) }).sum;
}
```

Curiously, it took me *ages* to get the `map`

right, first because I
initially used `pairs`

instead of `kv`

, which put me incredibly close to
the event horizon of a black hole from where I would have never escaped
(except, possibly, as Hawking radiation), and second because I was
insisting on round parentheses around `$x, $y`

, which are not needed
when using `->`

. Ouch.

This program gets the first **18** Disarium Numbers pretty quickly,
but it takes ages for the **19th**. Which is needed to complete the
challenge.

So yes, the code above will find the requested solutionâ€¦ *eventually*.
Yet it takes too much to accept it, even by *engineering* standards.

Iâ€™ll leave with a final note about the need for exactly 19 members of
the Disarium Numbers 20-members family. I mean, thatâ€™s being *mean*
in two senses:

- the 19th member is considerably greater than the first 18, which means that brute-force approaches will suffer (at least in languages that have margins for optimization);
- the 20th member
*feels excluded*. I mean, itâ€™s the last one and thereâ€™s no other after, why leave it outside in the cold? Or, well, in the heat, if youâ€™re in Roma these times?

See you next time!

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