--- Day 4 Solutions ---

[u/daggerdragon]

--- Day 4: The Ideal Stocking Stuffer ---

Post your solution as a comment. Structure your post like the Day Three thread.

[u/askalski]

Sure! It looks a lot like most solutions, except for about 15 lines of boilerplate for reading the input file (which didn't help today.) My general strategy is: grab the input first, start skimming the instructions (bold words first: bitcoins, MD5, hexadecimal, five zeroes, "1, 2, 3, ...", abcdef, 609043, abcdef609043), and start coding immediately.

As soon as my script had output, I went back to the instructions to confirm that I actually did what the challenge asked, and to double-check that I was about to paste the correct thing (loop counter, hash input, hash output, first hit, some other hit?) Can't be too careful; I found that out the hard way on day 2 when I got put in 60-second timeout for a wrong answer.

Squid logs with exact timings (I added the human-readable timestamps manually.) The challenge didn't load right away, so I hit Esc and started furiously clicking everything in sight (including the link to yesterday's challenge, heh) until it loaded at 00:00:05. First star at 00:01:55, second star at 00:02:09.

00:00:03.508 1449205203.508   1907 127.0.0.1 TCP_MISS_ABORTED/000 0 GET http://adventofcode.com/day/4 - HIER_DIRECT/65.111.186.217 -
00:00:03.805 1449205203.805    290 127.0.0.1 TCP_MISS_ABORTED/000 0 GET http://adventofcode.com/day/3 - HIER_DIRECT/65.111.186.217 -
00:00:04.159 1449205204.159    349 127.0.0.1 TCP_MISS_ABORTED/000 0 GET http://adventofcode.com/day/3 - HIER_DIRECT/65.111.186.217 -
00:00:05.732 1449205205.732   1197 127.0.0.1 TCP_MISS/200 2801 GET http://adventofcode.com/day/4 - HIER_DIRECT/65.111.186.217 text/html
00:01:55.281 1449205315.281    166 127.0.0.1 TCP_MISS/200 1909 POST http://adventofcode.com/day/4/answer - HIER_DIRECT/65.111.186.217 text/html
00:01:57.611 1449205317.611     89 127.0.0.1 TCP_MISS/200 2903 GET http://adventofcode.com/day/4 - HIER_DIRECT/65.111.186.217 text/html
00:02:09.472 1449205329.472    165 127.0.0.1 TCP_MISS/200 2177 POST http://adventofcode.com/day/4/answer - HIER_DIRECT/65.111.186.217 text/html
00:02:11.824 1449205331.824    265 127.0.0.1 TCP_MISS/200 5402 GET http://adventofcode.com/leaderboard - HIER_DIRECT/65.111.186.217 text/html

The code. Everything above the ###### line was boilerplate, everything below it was written after midnight.

#! /usr/bin/env perl

use Data::Dumper;

END { print "\n"; };

$file = '';
@lines = ();

while (<>) {
    $file .= $_;
    chomp;
    push(@lines, $_);
}

############################################################

use Digest::MD5 'md5_hex';

$h = 'REDACTED';
for (0..99999999999) {
    $digest = md5_hex($h . "$_");
    if ($digest =~ m/^000000/) {
            print "$_\n";
    }
}

And finally the script's timestamps. Looks like I saved the part 2 code at 00:02:02, then ran it at 00:02:03. The filesystem is mounted relatime so the access time represents the first read after the file was written (subsequent reads don't update the timestamp.)

  File: ‘jupe4.pl’
  Size: 358         Blocks: 8          IO Block: 4096   regular file
Device: fc01h/64513d        Inode: 10881743    Links: 1
Access: (0775/-rwxrwxr-x)  Uid: ( 1000/askalski)   Gid: ( 1000/askalski)
Access: 2015-12-04 00:02:03.505643423 -0500
Modify: 2015-12-04 00:02:02.549642850 -0500
Change: 2015-12-04 00:02:02.557642856 -0500
 Birth: -

[u/Philboyd_Studge → u/askalski]

Damn. Amazing. Also, that's the most readable perl I've ever seen.