# ETOOBUSY đźš€ minimal blogging for the impatient

# PWC149 - Fibonacci Digit Sum

**TL;DR**

Here we are with TASK #1 from The Weekly Challenge #149. Enjoy!

# The challenge

Given an input

`$N`

, generate the first`$N`

numbers for which the sum of their digits is a Fibonacci number.

Example`f(20)=[0, 1, 2, 3, 5, 8, 10, 11, 12, 14, 17, 20, 21, 23, 26, 30, 32, 35, 41, 44]`

# The questions

Wellâ€¦ this is nitpicking, Iâ€™ll read â€śnumbersâ€ť as â€śpositive integersâ€ť.

# The solution

Weâ€™ll start with Raku:

```
#!/usr/bin/env raku
use v6;
class FibonacciSumming { ... }
sub MAIN ($N = 20) {
my $fs = FibonacciSumming.new;
$fs.next.put for ^$N;
}
class FibonacciSumming {
has %!fibo = 0 => 1;
has $!f = 0;
has $!s = -1;
method next () {
while True {
++$!s;
my $sum = $!s.comb(/\d/).sum;
($!f, %!fibo{%!fibo{$!f}}) = %!fibo{$!f}, $!f + %!fibo{$!f}
while $!f < $sum;
return $!s if %!fibo{$sum}:exists;
}
}
}
```

We use an object to keep track of generating the outputs. There are three member variables:

`%!fibo`

keeps track of the â€śfollowingâ€ť number of Fibonacci numbers. I know that`1`

has two successors, but itâ€™s still working to indicate what is a Fibonacci number and what is not;`$!f`

is the companion to the hash above, keeping track of the latest key put in`%!fibo`

, so that we can generate more;`$!s`

is a candidate result.

The main method `next`

iterates until a suitable value is found in
`$!s`

. The `$sum`

is calculated according to the rules, then it is
checked against the Fibonacci numbers. The inner loop makes sure that
there are enough Fibonacci numbers to check for presence of `$sum`

The Perl version is *a sort* of translation, only weâ€™re opting for
an iterator function here instead of a full-fledged object:

```
#!/usr/bin/env perl
use 5.024;
use warnings;
use English qw< -no_match_vars >;
use experimental qw< postderef signatures >;
no warnings qw< experimental::postderef experimental::signatures >;
use List::Util 'sum';
my $it = fibonacci_summing();
say $it->() for 1 .. (shift || 20);
sub fibonacci_summing {
my %fibo = (0 => 1);
my $f = 0;
my $s = -1;
return sub {
while ('necessary') {
++$s;
my $sum = sum split m{}mxs, $s;
($f, $fibo{$fibo{$f}}) = ($fibo{$f}, $f + $fibo{$f})
while $f < $sum;
return $s if exists $fibo{$sum};
}
};
}
```

The returned `sub`

closes over `%fibo`

, `$f`

, and `$s`

, which have the
same exact role as in the Raku version.

I guess this is allâ€¦ until next time stay safe folks!

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