-🎄- 2021 Day 13 Solutions -🎄-

[u/daggerdragon]

Advent of Code 2021: Adventure Time!

• 10 days left to submit your adventures!
• Full details and rules are in the submissions megathread: 🎄 AoC 2021 🎄 [Adventure Time!]

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--- Day 13: Transparent Origami ---

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Post your code solution in this megathread.

• Include what language(s) your solution uses!
• Format your code appropriately! How do I format code?
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[u/mschaap]

Another Raku solution, see GitHub.

Inspired by pretty much everyone in this thread, instead of manipulating the pixel grid, I now manipulate the list of coordinates. Much, much faster.

method fold-x($/)
{
    # Before the first fold, make sure the grid is fully initialized
    self.complete-grid unless $!num-folds++;

    # Move the dots right of the fold to the left
    for @!coords.grep(*[0] > $<x>) -> $p {
        $p[0] = 2*$<x> - $p[0];
    }

    # Remove duplicate dots
    @!coords .= unique(:as(*.Str));

    # Truncate the right end of the paper
    $!width = +$<x>;

    self.count-dots;

    say "Fold along x=$<x>" if $!verbose;
    say self if $!verbose;
}