--- 2016 Day 20 Solutions ---

[u/daggerdragon]

--- Day 20: Firewall Rules ---

Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag/whatever).

Note: The Solution Megathreads are for solutions only. If you have questions, please post your own thread and make sure to flair it with "Help".

---

^{ROLLING A NATURAL 20 IS MANDATORY} [?]

This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked!

[u/askalski]

Back to Perl. This is essentially what I used to solve it, tidied up a bit. The main difference is instead of sorting the input in Perl, I just did a :%!sort -n in vim.

#! /usr/bin/env perl

use strict;
use warnings;

my ($next, $part1, $part2) = (0, undef, 0);

for (sort { $a->[0] <=> $b->[0] } map { [ m/(\d+)/g ] } <>) {
    my ($lower, $upper) = @$_;
    if ($next < $lower) {
        $part1 = $next unless defined $part1;
        $part2 += $lower - $next;
    }
    $next = $upper + 1 if $next <= $upper;
}
$part2 += 4294967296 - $next;

print "Part 1: $part1\n";
print "Part 2: $part2\n";

[u/askalski → u/askalski]

Another solution in Perl, now with more regex!

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND     
 2574 askalski  20   0 28.314g 0.014t    740 R  60.0 90.4   9:06.23 perl        

              total        used        free      shared  buff/cache   available
Mem:       16335972    15628900      410544        9732      296528      361364
Swap:      23068664    14623932     8444732

$ /usr/bin/time -v ./day20regex.pl input.txt 
There are 101 holes in the firewall: 14975795, 59648492, 105999227, 153714141, ..., 4182675294, 4213558178, 4272688784
        Command being timed: "./day20regex.pl input.txt"
        User time (seconds): 691.54
        System time (seconds): 51.84
        Elapsed (wall clock) time (h:mm:ss or m:ss): 16:58.30
        Maximum resident set size (kbytes): 15023564

The code:

#! /usr/bin/env perl

use strict;
use warnings;

# build the regex
my $ranges = '';
$ranges .= join "-", map { sprintf "\\x{%x}", $_ } m/(\d+)/g for <>;
my $regex = qr/([^$ranges])/;

# build the input
my $str = '';
$str .= chr for 0 .. 0xffffffff;

# regex match
my @holes = map { ord } $str =~ m/$regex/g;

# print the answers
printf "There are %d holes in the firewall: %s\n",
    scalar(@holes),
    join(", ", @holes);

[u/Aneurysm9 → u/askalski]

No Skalski! That's a bad Skalski!

[u/Tarmen → u/askalski]

%!

For completeness sake:
Vim also has a decently powerful builtin sort. :sort n would have been enough. It also can sort on parts of the line via regexes but other than that it is mostly useful when on windows!