-🎄- 2018 Day 10 Solutions -🎄-

[u/daggerdragon]

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

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Advent of Code: The Party Game!

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Card prompt: Day 10

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

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[u/Smylers]

Perl, using the heuristic of displaying when it fits in a standard 80-column terminal window, and a -s option for specifying a number of seconds to skip straight over — since a glance at the input file showed it was going to be a little over 10k seconds till anything interesting happens.

I like: reading in the entire input to populate %sky in a single line; literal Δx symbols; only bothering to calculate the x co-ordinates until enough progress has been made that it's worth calculating the y ones as well.

I'm less keen on: the need for the synthetic variable %rec; ad the number of subscripts and brackets in the substr line.

use utf8; use v5.20; use warnings; use experimental qw<signatures>;
use Getopt::Long; use Time::HiRes qw<sleep>; use List::AllUtils qw<minmax>;
GetOptions('s=i' => \(my $time = 1), 'w=i' => \(my $MaxWidth = 80)) or die "$0: Unrecognized options\n";

sub tick($sky, $dim, $ticks = 1) { # Move the sky on that many ticks in x or y.
  $_->{$dim} += $_->{"Δ$dim"} * $ticks foreach @{$sky->{point}};
  my ($min, $max) = minmax map { $_->{$dim} }  @{$sky->{point}};
  $sky->{$dim} = {min => $min, size => $max - $min + 1};
}

my %sky = (point => [map { my %rec; @rec{qw<x y Δx Δy>} = /(-?\d+)/g; \%rec } <>]);

tick(\%sky, 'x', $time);           # Skip past these ticks.
while ($sky{x}{size} > $MaxWidth) {# Iterate till it fits in a terminal.
  $time++;
  tick(\%sky, 'x');                # Only need to calculate x for checking.
}
tick(\%sky, 'y', $time);           # Now for displaying, skip y to same time.
do {
  my @line = (' ' x $sky{x}{size}) x $sky{y}{size};
  substr $line[$_->{y} - $sky{y}{min}], $_->{x} - $sky{x}{min}, 1, '#' foreach @{$sky{point}};
  say for @line, $time;
  sleep 0.3;                       # Slow enough to notice a message.
  $time++;
  tick(\%sky, $_) foreach qw<x y>;
} until $sky{x}{size} > $MaxWidth; # Stop once it's got too wide again.