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#!/usr/bin/env perl
use strict;
use warnings;
use experimental qw{ say postderef signatures state };
use Algorithm::Combinatorics qw{ variations };
my @examples = (
[ 8, 1, 9 ],
[ 8, 6, 7, 1, 0 ],
[1],
[ 9, 0, 1, 2, 5 ]
);
for my $e (@examples) {
my $input = join ', ', $e->@*;
my $output = largest_of_three( $e->@* );
say <<~"END";
Input: \$input = ($input)
Output: $output
END
}
sub largest_of_three (@input) {
my @output;
my $o = -1;
for my $c ( reverse 1 .. scalar @input ) {
my $iter = variations( \@input, $c );
while ( my $p = $iter->next ) {
my $combo = 0 + join '', $p->@*;
next if $combo % 3 != 0;
$o = $combo if $combo > $o;
}
}
return $o;
}
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