#!/usr/bin/perl

$filename = "11.txt";

open(FILE, $filename);
@data = <FILE>;
close(FILE);

@seats = ();

$maxrow = $#data;

# Read in the file
for ($a = 1; $a < ($maxrow + 2); $a++) {
        $line = $data[$a-1];
        $line =~ s/[^\.L]//sgi;
        @seatrow = split("", $line);
        $maxcolumn = $#seatrow;
        for ($b = 1; $b < ($maxcolumn + 2); $b++) {
                $seats[$a][$b] = $seatrow[$b-1];
        }
}

#Put floor around all the seats
for ($a = 0; $a < ($maxrow + 3); $a++) {
        $seats[$a][0] = ".";
        $seats[$a][$maxcolumn + 2] = ".";
}
for ($a = 0; $a < ($maxcolumn + 3); $a++) {
        $seats[0][$a] = ".";
        $seats[$maxrow + 2][$a] = ".";
}

$changed = 1;

@oldseats = ();
@ptseats = ();

#Make a copy of the 2-dimensional array (without references) for part2
for ($a = 0; $a < ($maxrow + 3); $a++) {
        for ($b = 0; $b < ($maxcolumn + 3); $b++) {
                $ptseats[$a][$b] = $seats[$a][$b];
        }
}

$rounds = 0;

#Loop until we make no changes.
while ($changed == 1) {
        $changed = 0;

        $rounds++;
        #Make a copy of the previous round, so we can change seats without affecting the current round.
        for ($a = 0; $a < ($maxrow + 3); $a++) {
                for ($b = 0; $b < ($maxcolumn + 3); $b++) {
                        $oldseats[$a][$b] = $seats[$a][$b];
                }
        }


        for ($a = 1; $a < ($maxrow + 2); $a++) {
                for ($b = 1; $b < ($maxcolumn + 2); $b++) {

                        #Floor - skip
                        if ($oldseats[$a][$b] eq ".") {
                                next;
                        }

                        #Vacant seat
                        if ($oldseats[$a][$b] eq "L") {

                                $isocc = 0;

                                #Check all 9 seats that is at the "cursor position". Since the middle seat isn't occupied, we don't need to except the middle seat from the checking.
                                for ($x = ($a - 1); $x < ($a + 2); $x++) {
                                        for ($y = ($b - 1); $y < ($b + 2); $y++) {
                                                if ($oldseats[$x][$y] eq "#") {
                                                        $isocc = 1;
                                                }
                                        }
                                }

                                if ($isocc == 0) {
                                        # Set the seat as occupied
                                        $seats[$a][$b] = "#";
                                        $changed = 1;
                                        next;
                                }
                        }

                        #occupied seat
                        if ($oldseats[$a][$b] eq "#") {

                                $isocc = 0;
                                #Count the number of occupied seats in the 8 adjacent seats.
                                for ($x = ($a - 1); $x < ($a + 2); $x++) {
                                        for ($y = ($b - 1); $y < ($b + 2); $y++) {
                                                #Skip the "cursor position"
                                                if (($x == $a)&&($y == $b)) {
                                                        next;
                                                }
                                                if ($oldseats[$x][$y] eq "#") {
                                                        $isocc++;
                                                }
                                        }
                                }
                                #More than 3 seats (4 or more) - set the seat as vacant
                                if ($isocc > 3) {
                                        $seats[$a][$b] = "L";
                                        $changed = 1;
                                }
                        }

                # End of for loops
                }
        }
}

# Part1 run finished - count number of occupied seats.

$counter = 0;

for ($a = 0; $a < ($maxrow + 3); $a++) {
        for ($b = 0; $b < ($maxcolumn + 3); $b++) {
                if ($seats[$a][$b] eq "#") {
                        $counter++;
                }
        }
}

print "Part 1 completed in $rounds rounds.\n";
print "P1: $counter \n";


#Part 2 run

$changed = 1;
@oldseats = ();

$rounds = 0;

#Loop until we make no changes
while ($changed == 1) {
        $rounds++;

        $changed = 0;

        # As before - make a copy so we can change seats without affecting the current round.
        for ($a = 0; $a < ($maxrow + 3); $a++) {
                for ($b = 0; $b < ($maxcolumn + 3); $b++) {
                        $oldseats[$a][$b] = $ptseats[$a][$b];
                }
        }

        for ($a = 1; $a < ($maxrow + 2); $a++) {
                for ($b = 1; $b < ($maxcolumn + 2); $b++) {

                        # Floor - skip
                        if ($oldseats[$a][$b] eq ".") {
                                next;
                        }


                        #Vacant seat
                        if ($oldseats[$a][$b] eq "L") {

                                $isocc = 0;

                                #Loop through all positions adjacent to the seat - but this time, only relative positions.
                                for ($x = -1; $x < 2; $x++) {
                                        for ($y = -1; $y < 2; $y++) {
                                                #If relative position means no change, skip
                                                if (($x == 0)&&($y == 0)) {
                                                        next;
                                                }

                                                # Shoot a "laser" in that direction. This by adding the relative change to the current "cursor" position.
                                                $tally = $b + $y;
                                                for ($d = $a + $x; (($d > 0)&&($d < ($maxrow + 3))); $d = $d + $x) {
                                                        # If we go out of bounds in Y direction, end the for loop.
                                                        # This means, that even if $x in the for loop is 0 - it will still not be a infinite loop.
                                                        if (($tally < 1)||($tally > ($maxcolumn + 2))) {
                                                                last;
                                                        }
                                                        # If we stumble upon a vacant seat, end the for loop.
                                                        if ($oldseats[$d][$tally] eq "L") {
                                                                last;
                                                        }
                                                        # If we stumble upon a occupied seat, set the flag and end for loop.
                                                        if ($oldseats[$d][$tally] eq "#") {
                                                                $isocc = 1;
                                                                last;
                                                        }
                                                        #For each change in X direction, change also in Y direction.
                                                        $tally = $tally + $y;
                                                }

                                        }
                                }
                                # If all "lasered" seats are vacant, set seat as occupied.
                                if ($isocc == 0) {
                                        $ptseats[$a][$b] = "#";
                                        $changed = 1;
                                        next;
                                }
                        }

                        # Occupied seat
                        if ($oldseats[$a][$b] eq "#") {

                                $isocc = 0;
                                # Same here, loop through all positions adjacent to the seat, but here, only saving relative positions.
                                for ($x = -1; $x < 2; $x++) {
                                        for ($y = -1; $y < 2; $y++) {
                                                # If the relative position are no change, skip.
                                                if (($x == 0)&&($y == 0)) {
                                                        next;
                                                }

                                                # Shoot a "laser" in that direction. This by adding the relative change to the current "cursor" position.
                                                $tally = $b + $y;
                                                for ($d = $a + $x; (($d > 0)&&($d < ($maxrow + 3))); $d = $d + $x) {
                                                        # If we go out of bounds in Y direction, end the for loop.
                                                        # This means, that even if $x in the for loop is 0 - it will still not be a infinite loop.
                                                        if (($tally < 1)||($tally > ($maxcolumn + 2))) {
                                                                last;
                                                        }

                                                        #If we find a vacant seat, end the for loop.
                                                        if ($oldseats[$d][$tally] eq "L") {
                                                                last;
                                                        }
                                                        #If we find a occupied seat, add to the count and end the for loop.
                                                        if ($oldseats[$d][$tally] eq "#") {
                                                                $isocc++;
                                                                last;
                                                        }
                                                        #For each change in X direction, change also in Y direction.
                                                        $tally = $tally + $y;
                                                }

                                        }
                                }
                                # If number of occupied seats exceed 4 (5 or more) then set the seat as vacant.
                                if ($isocc > 4) {
                                        $ptseats[$a][$b] = "L";
                                        $changed = 1;
                                }
                        }

                # End of for loops
                }
        }
}

#Finished part 2 run - Count number of occupied seats.

$counter = 0;

for ($a = 0; $a < ($maxrow + 3); $a++) {
        for ($b = 0; $b < ($maxcolumn + 3); $b++) {
                if ($ptseats[$a][$b] eq "#") {
                        $counter++;
                }
        }
}

print "Part 2 completed in $rounds rounds.\n";
print "P2: $counter \n";