Fun little regex exercise :)

#!/usr/bin/perl

# http://perlmonks.org/?node_id=1211497

use strict;
use warnings;

my $triangle = <<END;
               0-0
            1-0   1-1
         2-0   2-1   2-2
      3-0   3-1   3-2   3-3
   4-0   4-1   4-2   4-3   4-4
5-0   5-1   5-2   5-3   5-4   5-5
END

$^R = '3-1';  # clicked node

"@{[ reverse split /\n/, $triangle ]}" =~ / $^R
  (?: .*
    ((??{
      my ($row, $col) = split m{\D}, $^R;
      $row ? ($row - 1) . '-[' . ($col > 0 && $col - 1) . "$col]" : '(
+*F)'
      }))
    (?{$1 eq '0-0' and print "$1 $^R\n"; "$1 $^R"})
  )+
  (*F)
  /x;
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