--- /dev/null
+#!/usr/bin/perl -w
+
+use v5.16;
+
+my @m = map { chomp; [ split // ] } <>;
+
+my $sum;
+for (1 .. 100) {
+ my %f;
+ my @q;
+ for my $x (0 .. 9) {
+ for my $y (0 .. 9) {
+ next if $f{$x,$y};
+ next if ++$m[$y][$x] < 10;
+ $f{$x,$y} = 1;
+ push @q, [$x,$y];
+ say "flashed:$x,$y";
+ } }
+ while (@q) {
+ my $p = shift @q;
+ my ($x2, $y2) = @$p;
+
+ for my $dx (-1 .. 1) {
+ for my $dy (-1 .. 1) {
+ next if $dx == 0 && $dy == 0;
+ next if $x2+$dx < 0 || $x2+$dx > 9;
+ next if $y2+$dy < 0 || $y2+$dy > 9;
+ next if $f{$x2+$dx,$y2+$dy};
+ say $x2+$dx, ',', $y2+$dy, ' >',$m[$y2+$dy][$x2+$dx];
+ next if ++$m[$y2+$dy][$x2+$dx] < 10;
+ $f{$x2+$dx,$y2+$dy} = 1;
+ push @q, [$x2+$dx, $y2+$dy];
+ say "flashed ", $x2+$dx,',',$y2+$dy;
+ } }
+ }
+ for my $p (keys %f) {
+ my ($x, $y) = split /$;/, $p;
+ $m[$y][$x] = 0;
+ }
+ say "Step $_ flashes ", scalar keys %f;
+ say join("\n", map { join('', @$_) } @m);
+ say;
+ # last if $_ > 1;
+ $sum += keys %f;
+}
+
+say $sum;
+
--- /dev/null
+#!/usr/bin/perl -w
+
+use v5.16;
+
+my @m = map { chomp; [ split // ] } <>;
+
+my $sum;
+my $step = 0;
+while (++$step) {
+ my %f;
+ my @q;
+ for my $x (0 .. 9) {
+ for my $y (0 .. 9) {
+ next if $f{$x,$y};
+ next if ++$m[$y][$x] < 10;
+ $f{$x,$y} = 1;
+ push @q, [$x,$y];
+ say "flashed:$x,$y";
+ } }
+ while (@q) {
+ my $p = shift @q;
+ my ($x2, $y2) = @$p;
+
+ for my $dx (-1 .. 1) {
+ for my $dy (-1 .. 1) {
+ next if $dx == 0 && $dy == 0;
+ next if $x2+$dx < 0 || $x2+$dx > 9;
+ next if $y2+$dy < 0 || $y2+$dy > 9;
+ next if $f{$x2+$dx,$y2+$dy};
+ say $x2+$dx, ',', $y2+$dy, ' >',$m[$y2+$dy][$x2+$dx];
+ next if ++$m[$y2+$dy][$x2+$dx] < 10;
+ $f{$x2+$dx,$y2+$dy} = 1;
+ push @q, [$x2+$dx, $y2+$dy];
+ say "flashed ", $x2+$dx,',',$y2+$dy;
+ } }
+ }
+ for my $p (keys %f) {
+ my ($x, $y) = split /$;/, $p;
+ $m[$y][$x] = 0;
+ }
+ say "Step $_ flashes ", scalar keys %f;
+ say join("\n", map { join('', @$_) } @m);
+ say;
+ last if keys %f == 100;
+}
+
+say $step;
+