Challenge 61: Products and Addresses
Perl Weekly Challenge #61, with answers reversed because I want to.
TASK #2 › IPv4 Partition
Reviewed by: Ryan Thompson
You are given a string containing only digits (0..9). The string should have between 4 and 12 digits.
Write a script to print every possible valid IPv4 address that can be made by partitioning the input string.
For the purpose of this challenge, a valid IPv4 address consists of four “octets” i.e. A, B, C and D, separated by dots (.).
Each octet must be between 0 and 255, and must not have any leading zeroes. (e.g., 0 is OK, but 01 is not.)
Example Input:
25525511135Output:
255.255.11.135
255.255.111.35
Should we still deal with IPv4 addresses anymore? Vint Cerf argues no.
But, since it’s the challenge, let’s go.
#!/usr/bin/env perl
use strict;
use warnings;
use utf8;
use feature qw{ postderef say signatures state switch };
no warnings qw{ experimental };
my $input = '25525511135';
($input) = $ARGV[0] =~ /(\d+)/ if defined $ARGV[0];
my @input = split //, $input;
my $output = '';
say join "\n\t", "$input =>", ipv4_partitions( $output, @input );
sub ipv4_partitions ( $output, @input ) {
# this block ensures we only have "good" addresses go through
# * no .1.1.1.1
# * only four numbers
# * only three periods
# * no number greater than 255
# ( because only digits, no need to block negatives)
# * no zero-pads - 0 is fine, 04 is not
return if $output =~ /^\./;
return if 4 < scalar split /\./, $output;
return if grep { int $_ > 255 } split /\./, $output;
return if grep { length $_ > 3 } split /\./, $output;
return if grep { $_ =~ /0\d/ } split /\./, $output;
my @zed;
# if there's still digits to fit
if ( scalar @input ) {
my $next = shift @input;
push @zed, ipv4_partitions( qq{$output\.$next}, @input );
push @zed, ipv4_partitions( qq{$output$next}, @input );
}
else {
# handles non-\d+.\d+.\d+.\d+ cases
return if 4 != scalar split /\./, $output;
push @zed, $output;
}
return @zed;
}
There’s one IP address that I doubt I ever will forget, which is for the main DNS server for my former school and workplace. This is a good example because it shows what is and isn’t allowed with zeroes.
./ch-2.pl 128210115
128210115 =>
1.28.210.115
12.8.210.115
12.82.10.115
128.2.10.115
128.21.0.115
128.210.1.15
128.210.11.5
TASK #1 › Product SubArray
Reviewed by: Ryan Thompson
Given a list of 4 or more numbers, write a script to find the contiguous sublist that has the maximum product. The length of the sublist is irrelevant; your job is to maximize the product.
Example
Input:
[ 2, 5, -1, 3 ]Output:
[ 2, 5 ]which gives maximum product10.
I’m usng JSON to format the output.
$ ./ch-1.pl 2 5 1 5 2
["2","5"]
Both [2,5] and [5,2] are valid as max, but we return [2,5] because it comes first.
#!/usr/bin/env perl
use strict;
use warnings;
use utf8;
use feature qw{ postderef say signatures state switch };
no warnings qw{ experimental };
use JSON;
my $json = JSON->new;
my @numbers = @ARGV;
@numbers = ( 2, 5, -1, 3 ) if scalar @ARGV < 4;
my @array = product_subarray(@numbers);
say $json->encode(@array);
exit;
sub product_subarray ( @numbers ) {
my @output;
for my $i ( 1 .. $#numbers ) {
my $j = $i - 1;
my $product = $numbers[$j] * $numbers[$i];
push @output, { p => $product, n => [ $numbers[$j], $numbers[$i] ], };
}
my ($output) = sort { $b->{p} <=> $a->{p} } @output;
return $output->{n};
}