Advent Calendar - December 7, 2020

Advent Calendar 2020

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The gift is presented by Javier Luque. Today he is talking about his solution to the task IPv4 Partition of “The Weekly Challenge - 061”. This is re-produced for Advent Calendar 2020 from the original post by Javier Luque.

IPv4 Partition

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: 25525511135,

Output:

255.255.11.135
255.255.111.35

For this challenge I brute forced the solution my finding all the possible locations of the . then checking the string if its a valid IP address.

so a string like: 12345

Will produce these combinations

    1.2.3.45
    1.2.34.5
    1.23.4.5
    12.3.4.5

Perl

#!/usr/bin/perl
# Test: ./ch-2.pl
use strict;
use warnings;
use feature qw /say/;
use Algorithm::Combinatorics qw(combinations);

my $ip_address = $ARGV[0] || '25525511135';
partition_ip_string($ip_address);

# Partition the ip string
sub partition_ip_string {
    my $string = shift;
    my $length = length($string) - 2;

    # Validate string
    return undef if
        ( length($string) < 4  ||
          length($string) > 12 ||
          !($string =~ /^\d+$/)
        );

    # Find all the combinations for the possible ips
    my @dot_positions = (0 .. $length);
    my $iter = combinations(\@dot_positions, 3);

    # Process the combinations
    while (my $combos = $iter->next) {
        my $to_test = $string;
        my $offset = 0;

        for my $dot_position (@$combos) {
            my $position =
            	($dot_position + $offset) + 1;

            # Append to the test string;
            $to_test =
            	(substr $to_test, 0, $position)
            	. '.' .
            	(substr $to_test, $position);

            # Offset the string
            $offset++;
        }

        say $to_test
            if (validate_ip_string($to_test));
    }
}

# Validate the IP String
sub validate_ip_string {
    for my $digit (split('\.', shift)) {
        return 0 if ($digit > 255);
        return 0 if ($digit =~ /^0\d+$/);
    }

    return 1;
}

Output perl ch-2.pl

255.255.11.135
255.255.111.35

Raku

# Test: perl6 ch-2.p6
multi MAIN() {
    MAIN('25525511135');
}

multi MAIN(Str $str) {
    partition-ip-string($str);
}

# Partition the ip string
sub partition-ip-string (Str $str) {
    my $length = $str.chars - 2;

    # Find all the combinations for the possible ips
    my @dot_positions = (0 .. $length);
    my @combos = @dot_positions.combinations: 3;

    # Process the combinations
    for @combos -> @combo {
        my $to_test = $str;
        my $offset = 0;

        for (@combo) -> $dot_position {
            my $position =
            	($dot_position + $offset) + 1;

            # Append to the test string;
            $to_test =
            	$to_test.substr(0, $position)
            	~ '.' ~
            	$to_test.substr($position);

            # Offset the string
            $offset++;
        }

        say $to_test
            if (validate-ip-string($to_test));
    }
}

# Validate the IP String
sub validate-ip-string(Str $str) {
    for $str.split('.') -> $digit {
        return False if ($digit > 255);
        return False if ($digit ~~ /^0\d+$/);
    }
    return True;
}

Output perl6 ch-2.p6

255.255.11.135
255.255.111.35

If you have any suggestion then please do share with us perlweeklychallenge@yahoo.com.

Advent Calendar 2020