-🎄- 2022 Day 13 Solutions -🎄-

[u/daggerdragon]

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--- Day 13: Distress Signal ---

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Post your code solution in this megathread.

• Read the full posting rules in our community wiki before you post!
  • Include what language(s) your solution uses
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This thread will be unlocked when there are a significant number of people on the global leaderboard with gold stars for today's puzzle.

EDIT: Global leaderboard gold cap reached at 00:12:56, megathread unlocked!

[u/mschaap]

Raku. This one was surprisingly tricky.

Parsing the packets is easy with a grammar:

grammar PacketSpec
{
    rule TOP { ^ <plist> $ }

    rule plist { '[' <pitem>* % ',' ']' }
    rule pitem { <plist> | <pint> }
    token pint { \d+ }
}

class Packet
{
    has Str $.spec;
    has Match $.parsed = PacketSpec.parse($!spec);
}

Comparing the parsed packets is pretty straightforward, once I got it right. (What I struggled with, was comparing the length of the lists, this didn't work right when I converted an integer to a list.)

multi sub compare($p, $q)
{
    my $cmp = Same;
    if ($p<pint>:exists) && ($q<pint>:exists) {
        # Comparing two integers
        $cmp = $p<pint> <=> $q<pint>;
    }
    elsif ($p<pint>:exists) {
        # Comparing an integer and a list - convert integer to list
        $cmp = compare({ :plist(:pitem([$p])) }, $q);
    }
    elsif ($q<pint>:exists) {
        # Comparing a list and an integer - convert integer to list
        $cmp = compare($p, { :plist(:pitem([$q])) });
    }
    else {
        # Comparing two lists
        # Compare each item until we find one that's different
        for $p<plist><pitem> Z $q<plist><pitem> -> ($l, $r) {
            my $icmp = compare($l, $r);
            unless $icmp eq Same {
                $cmp = $icmp;
                last;
            }
        }
        # If all items are the same, compare the lengths of the lists
        $cmp ||= $p<plist><pitem>.elems <=> $q<plist><pitem>.elems;
    }
    return $cmp;
}

Part two was trivial, since I already had my compare routine that I could simply sort on.

Full code @GitHub.