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#!/usr/bin/perl
#
# Perl Weekly Challenge - 068
#
# Task #2: Reorder List
#
# https://perlweeklychallenge.org/blog/perl-weekly-challenge-068/
#
package Node;
use Moo;
has v => (is => 'rw');
has c => (is => 'rw');
sub show_link {
my ($self) = @_;
my $head = $self;
my @v = ();
while ($head->c) {
push @v, $head->v;
$head = $head->c;
}
push @v, $head->v;
return sprintf("%s", join ' -> ', @v);
}
package main;
use Test::More;
is( reorder_list('1 -> 2 -> 3 -> 4')->show_link,
'1 -> 4 -> 2 -> 3',
'testing 1 -> 2 -> 3 -> 4' );
is( reorder_list('1 -> 2 -> 3 -> 4 -> 5')->show_link,
'1 -> 5 -> 2 -> 4 -> 3',
'testing 1 -> 2 -> 3 -> 4 -> 5' );
is( reorder_list('1 -> 2 -> 3 -> 4 -> 5 -> 6')->show_link,
'1 -> 6 -> 2 -> 5 -> 3 -> 4',
'testing 1 -> 2 -> 3 -> 4 -> 5 -> 6' );
done_testing;
#
#
# METHODS
sub reorder_list {
my ($list) = @_;
$list =~ s/\s+//g;
$list = [ split /\-\>/, $list ];
my $head = Node->new(v => shift @$list);
my $link = [ $head ];
# prepare singly linked list
foreach my $v (@$list) {
my $node = Node->new(v => $v);
$link->[-1]->c($node);
push @$link, $node;
}
# reorder linked list
my $i = 1;
foreach (0 .. int($#$list/2)) {
my $node = pop @$link;
splice(@$link, $i, 0, $node);
# remove child from the last node
$link->[-1]->c(undef);
# link new node to previous node
$link->[$i-1]->c($node);
# make the next node as child of new node
$node->c($link->[$i+1]);
$i += 2;
}
return $head;
}
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