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use warnings;
use strict;
use feature ":5.26";
## ## ## ## ## MAIN:
## acquire the locus value and the array representation
## of the linked list
my ($locus, @input) = @ARGV;
my $next = undef;
my $node;
## 1. convert the input commandline array into a linked list
while (scalar @input > 0) {
my $value = pop @input;
$node = new Node($value, $next);
$next = $node
}
## $node currently points to beginning of the list
my $prelist_first;
my $prelist_last;
my $postlist_first;
my $postlist_last;
while (defined $node) {
## 2a. if it is less than the given value, add it to
## the end of the pre list
if ($node->value < $locus) {
defined $prelist_last ? $prelist_last->next($node)
: ($prelist_first = $node);
$prelist_last = $node;
}
## 2b. if it is more than or equal to the given value
## add it to the end of the post list
else {
defined $postlist_last ? $postlist_last->next($node)
: ($postlist_first = $node);
$postlist_last = $node;
}
$node = $node->next;
}
## 3. link the pre list to the post list:
## 3a. point the last element of the pre list to
## the first element of the post
$prelist_last->next($postlist_first) if (defined $prelist_last);
## 3b. point the last element of the post list to null
$postlist_last->{'next'} = undef;
## ## ## output
## if prelist never got made, start with the postlist
$node = $prelist_first || $postlist_first;
my @output;
while (defined $node) {
push @output, $node->value;
$node = $node->next;
}
say join ' → ', @output;
## ## ## ## ## NODE PACKAGE
package Node;
sub new {
my ($class, $value, $next) = @_;
my $self = { "value" => $value,
"next" => $next };
bless $self, $class;
return $self;
}
sub value {
my ($self, $value ) = @_;
$self->{value} = $value if defined $value;
return $self->{value}
}
sub next {
my ($self, $next ) = @_;
$self->{next} = $next if defined $next;
return $self->{next}
}
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