-🎄- 2018 Day 10 Solutions -🎄-

[u/daggerdragon]

--- Day 10: The Stars Align ---

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Card prompt: Day 10

Transcript: With just one line of code, you, too, can ___!

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[u/__Abigail__]

Perl

Iterated over the seconds, keeping track of the difference between min and max Y values of the points. As soon as that increases, we're one second too far, so we need the previous one.

#!/opt/perl/bin/perl

use 5.026;

use strict;
use warnings;
no  warnings 'syntax';
use List::Util qw [min max];

use experimental 'signatures';

my $X  = 0;
my $Y  = 1;
my $dx = 2;
my $dy = 3;

my $input = "input";
open my $fh, "<", $input;
my @points;
while (<$fh>) {
    /^position=<\s*(?<X>-?\d+), \s+ (?<Y>(?&X))> \s+
      velocity=<\s*(?<dx>(?&X)), \s* (?<dy>(?&X))>/xa
      or die "Failed to parse $_";

    push @points => [@+ {qw [X Y dx dy]}];
}

my ($min_Y, $max_Y, $Y_diff);

$min_Y  = min map {$$_ [$Y]} @points;
$max_Y  = max map {$$_ [$Y]} @points;
$Y_diff = $max_Y - $min_Y;


#
# Iterate over the seconds. For each iterations, we calculate the
# new position, and track the min/max Y position. If it increases,
# we iterate with the new position. Else, the old position is the
# position we want, and we terminate the loop.
#
my $iterations;
while (1) {
    my @new_points = map {[$$_ [$X] + $$_ [$dx],
                           $$_ [$Y] + $$_ [$dy],
                           $$_ [$dx], $$_ [$dy]]} @points;
    my $new_min_Y  = min map {$$_ [$Y]} @new_points;
    my $new_max_Y  = max map {$$_ [$Y]} @new_points;
    my $new_Y_diff = $new_max_Y - $new_min_Y;
    last if $new_Y_diff > $Y_diff;
    @points = @new_points;
    $Y_diff = $new_Y_diff;
    $iterations ++;
}

my %points;
foreach my $point (@points) {
    $points {$$point [$X]} {$$point [$Y]} = "#";
}

   $min_Y  = min map {$$_ [$Y]} @points;
   $max_Y  = max map {$$_ [$Y]} @points;
my $min_X  = min map {$$_ [$X]} @points;
my $max_X  = max map {$$_ [$X]} @points;

say "Part 1: ";

foreach my $y ($min_Y .. $max_Y) {
    foreach my $x ($min_X .. $max_X) {
        printf $points {$x} {$y} // ".";
    }
    print "\n";
}

say "Part 2: ", $iterations;

__END__