Day 9: Mirage Maintenance

Megathread guidelines

  • Keep top level comments as only solutions, if you want to say something other than a solution put it in a new post. (replies to comments can be whatever)
  • Code block support is not fully rolled out yet but likely will be in the middle of the event. Try to share solutions as both code blocks and using something such as https://topaz.github.io/paste/ , pastebin, or github (code blocks to future proof it for when 0.19 comes out and since code blocks currently function in some apps and some instances as well if they are running a 0.19 beta)

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  • @voleEnglish
    2•1 year ago

    Raku

    First time using Grammar Actions Object to make parsing a little cleaner. I thought about not keeping track of the left and right values (and I originally didn’t for part 1), but I think keeping track allows for an easier to understand solution.

    View code on github

    edit: although I don’t know why @values.all != 0 evaluates to true why any value is not zero. I thought that @values.any != 0 would do that, but it seems that their behavior is flipped from my expectations.

    edit2: Oh, I think I understand now. != is a shortcut for !==, and !== is actually the equality operator that is then negated. You can negate most relational operators in Raku by prefixing them with !. So the junction is actually binding to the == equality operator and not the !== inequality operator. Therefore @values.all != 0 becomes !(@values.all == 0). I’m not sure why they would choose this order of operations, though.

    edit3: Ah, it’s in the documentation, so it’s not even an oversight. https://github.com/rakudo/rakudo/issues/3748

    Code (probably still doesn't render correctly) 
    use v6;

sub MAIN($input) {
    my $file = open $input;

    grammar Oasis {
        token TOP { +%"\n" "\n"* }
        token history { +%\h+ }
        token val { '-'? \d+ }
    }

    class OasisActions {
        method TOP ($/) { make $».made }
        method history ($/) { make $».made }
        method val ($/) { make $/.Int }
    }

    my $oasis = Oasis.parse($file.slurp, actions => OasisActions.new);
    my @histories = $oasis.made;
    my $part-one-solution;
    my $part-two-solution;
    sub revdiff { $^b - $^a }
    for @histories -> @history {
        my @values = @history;
        my @rightmosts = [@values.tail];
        my @leftmosts = [@values.head];
        while @values.all != 0 {
            @values = @values.tail(*-1) Z- @values.head(*-1);
            @rightmosts.push(@values.tail);
            @leftmosts.push(@values.head);
        }
        $part-one-solution += [+] @rightmosts;
        $part-two-solution += [[&revdiff]] @leftmosts.reverse;
    }
    say "part 1: $part-one-solution";
    say "part 2: $part-two-solution";
}