aoc2021

commit 8e66f05b398baf40c15fa401b840a2f8b9874753
parent bc0e4535045530a200ecbcef4bbaacc5d6cf141f
Author: Samir Parikh <noreply@samirparikh.com>
Date:   Tue, 21 Dec 2021 16:49:13 +0000

get day09-2.pl to provide working solution for Day 09 Part 2

Diffstat:
M
day09-2.pl
 | 
26
+++++++++++++++++++-------

1 file changed, 19 insertions(+), 7 deletions(-)
diff --git a/day09-2.pl b/day09-2.pl
@@ -13,8 +13,10 @@ sub find_basin {
     my $location = shift @queue;
     my $r = $location->[0];
     my $c = $location->[1];
-    my $location_height = $heightmap_ref->[$r][$c];
+    my $location_height = $heightmap_ref->[$r][$c]; # can delete later
     say "checking location of $r, $c with height of $location_height";
+    # don't want to double-count the initial lowpoint
+    $heightmap_ref->[$r][$c] = 9;
     # check surrounding locations for increase in height
     foreach my $offset ([0, -1], [0, 1], [-1, 0], [1, 0]) {
       my $neighbor_row     = $r + $offset->[0];
@@ -22,11 +24,14 @@ sub find_basin {
       my $neighbor_height = $heightmap_ref->[$neighbor_row][$neighbor_col];
       say "neighbor at $neighbor_row, $neighbor_col has height $neighbor_height";
       next if ($neighbor_height == 9);
-      if ($neighbor_height == $location_height + 1) { # found increase
-        say "found winner";
-        push @queue => [ $neighbor_row, $neighbor_col ]; # add neighbor to queue
-        $size++;
-      }
+      #if ($neighbor_height == $location_height + 1) { # found increase
+      say "found winner";
+      # add neighbor coordinates to queue and set its height to 9 to prevent
+      # it from being checked again (double-counted)
+      push @queue => [ $neighbor_row, $neighbor_col ]; # add neighbor to queue
+      $heightmap_ref->[$neighbor_row][$neighbor_col] = 9;
+      $size++;
+      #}
     }
   }
   #say "row is $location->[0] and column is $location->[1]";
@@ -40,6 +45,7 @@ my $columns = @{$heightmap[0]};
 push @heightmap => [ (9) x $columns ]; # add extra row of 9s
 my $rows = @heightmap;
 my $risk_level = 0;
+my @basin_sizes;
 
 foreach my $row (0 .. $rows - 2) { # don't care about last row that we added
   foreach my $column (0 .. $columns - 2) { # don't care about the last column
@@ -54,12 +60,18 @@ foreach my $row (0 .. $rows - 2) { # don't care about last row that we added
     }
     # found low point
     if ($lowpoint) {
-      say "found lowpoint of height $height at $row, $column";
+      say "======================================";
+      say "found lowpoint at $row, $column with height of $height";
       $risk_level += $height + 1;
       my $basin_size = find_basin( $row, $column, \@heightmap );
       say "basin size is $basin_size";
+      push @basin_sizes => $basin_size;
     }
   }
 }
 
 say $risk_level;
+# plain `sort` routine just sorts by strings in code point order
+@basin_sizes = sort { $a <=> $b} @basin_sizes;
+say "@basin_sizes";
+say $basin_sizes[-3] * $basin_sizes[-2] * $basin_sizes[-1];