As
koolade pointed out, not all of these
work. Yours in particular goes into deep recursion.
Works in theory is not good enough, in golf you are going
to learn a lot about the assumptions you cannot make.
And yours has at least 2 separate (and serious) mistakes.
BTW the counts as I list them are just for the body of the
sub, so if yours did work it would be 51 characters.
Playing independently I came in with several solutions
that are small, and the following which is similar to
yours really does work at 58:
sub f {
my($s,$t)=@_;$t?$$t{d}eq$s?$t:f($s,$$t{l})||f($s,$$t{r}):0
}
And here, thanks to
koolade, is the test that I use:
$t = {
d => 'd',
l => {
d => 'b',
l => { d => 'a', l => 0, r => 0, },
r => { d => 'c', l => 0, r => 0, },
},
r => {
d => 'f',
l => { d => 'e', l => 0, r => 0, },
r => { d => 'g', l => 0, r => 0, },
}
};
sub test {
my $val = f(@_);
print $val ? "$val->{d}:$val\n" : "$val\n";
}
test('e',$t);
test('O',$t);