#!perl -w
use strict;
sub choose {
my ($str, $n) = @_;
my @result;
choose1(\@result, "", $str, $n, 0);
return @result;
}
sub choose1 {
my ($parray, $this, $str, $n, $x) = @_;
if ($n == 0) {
push @{$parray}, $this;
return;
}
return if $x + $n > length($str);
choose1($parray, $this . substr($str, $x, 1), $str, $n - 1, $x+1);
choose1($parray, $this, $str, $n, $x+1);
}
my %edges;
my %nodes;
my %collinear;
for (qw(ab acfi adgj ae bcde bfhj bi ej eghi ij)) {
$nodes{$_} = 1 for choose($_, 1);
$edges{$_} = 1 for choose($_, 2);
$collinear{$_} = 1 for choose($_, 3);
}
my $allnodes = join "", sort keys %nodes;
for my $triple (grep {!$collinear{$_}} choose($allnodes, 3)) {
print "$triple\n" if 3 == grep { $edges{$_} } choose($triple, 2);
}