Day 9: Mirage Maintenance

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  • @vole@lemmy.worldEnglish
    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";
}