# 2023 AoC Day 16 – The Floor Will Be Lava

This is a solution to Advent of Code 2023 day 16, written in Raku.

### Part One

The light isn't energizing enough tiles to produce lava; to debug the contraption, you need to start by analyzing the current situation. With the beam starting in the top-left heading right, how many tiles end up being energized?

constant \size = 110;
my @grid[size;size] = '16-input.txt'.IO.lines>>.comb;
my @energized[size;size];
my %visited;

enum Direction <North East South West>;

sub trace($x is copy,$y is copy, $dir is copy) { loop { @energized[$y;$x] = '#'; given @grid[$y;$x] { when '\\' { given$dir {
when North { $dir = West; } when South {$dir = East; }
when East { $dir = South; } when West {$dir = North; }
}
}
when '/' {
given $dir { when North {$dir = East; }
when South { $dir = West; } when East {$dir = North; }
when West { $dir = South; } } } when '|' { given$dir {
when East | West {
trace($x,$y, North);
trace($x,$y, South);
return;
}
}
}
when '-' {
given $dir { when North | South { trace($x, $y, East); trace($x, $y, West); return; } } } } given$dir {
when North { $y -= 1; return if$y < 0; }
when South { $y += 1; return if$y >= size; }
when East { $x += 1; return if$x >= size; }
when West { $x -= 1; return if$x < 0; }
}
return if %visited{"{$x},{$y},{$dir}"}:exists; %visited{"{$x},{$y},{$dir}"} = True;
}
}
trace(0, 0, East);
my $total = +@energized.grep(->$c { $c.defined &&$c eq '#'} );
say "Total energized {$total}"; Total energized 6994  ### Part Two So, the beam could start on any tile in the top row (heading downward), any tile in the bottom row (heading upward), any tile in the leftmost column (heading right), or any tile in the rightmost column (heading left). To produce lava, you need to find the configuration that energizes as many tiles as possible. Find the initial beam configuration that energizes the largest number of tiles; how many tiles are energized in that configuration? constant \size = 110; my @grid[size;size] = '16-input.txt'.IO.lines>>.comb; enum Direction <North East South West>; sub trace-config($x, $y,$dir) {
my @energized[size;size];
my %visited;
sub trace($x is copy,$y is copy, $dir is copy) { loop { @energized[$y;$x] = '#'; given @grid[$y;$x] { when '\\' { given$dir {
when North { $dir = West; } when South {$dir = East; }
when East { $dir = South; } when West {$dir = North; }
}
}
when '/' {
given $dir { when North {$dir = East; }
when South { $dir = West; } when East {$dir = North; }
when West { $dir = South; } } } when '|' { given$dir {
when East | West {
trace($x,$y, North);
trace($x,$y, South);
return;
}
}
}
when '-' {
given $dir { when North | South { trace($x, $y, East); trace($x, $y, West); return; } } } } given$dir {
when North { $y -= 1; return if$y < 0; }
when South { $y += 1; return if$y >= size; }
when East { $x += 1; return if$x >= size; }
when West { $x -= 1; return if$x < 0; }
}
return if %visited{"{$x},{$y},{$dir}"}:exists; %visited{"{$x},{$y},{$dir}"} = True;
}
}

trace($x,$y, $dir); +@energized.grep(->$c { $c.defined &&$c eq '#' })
}

my @totals = (^size).map(-> $x { trace-config($x, 0, South); });
@totals.append: (^size).map(-> $x { trace-config($x, size - 1, North); });
@totals.append: (^size).map(-> $y { trace-config(0,$y, East); });
@totals.append: (^size).map(-> $y { trace-config(size - 1,$y, West); });

say "Total energized in best configuration {@totals.max}";
say "Took " ~ (now - ENTER now).base(10,2) ~ " seconds";
Total energized in best configuration 7488
Took 28.78 seconds