note koolade <p>I haven't been able to get some of the answers to work. Maybe I have a different image of the data structure. Can somebody post what they've been working with? <p>Here's what I'm using to test: <code> $t = { d => 'd', l => { d => 'b', l => { d => 'a', l => 0, r => 0, }, r => { d => 'c', l => 0, r => 0, }, }, r => { d => 'f', l => { d => 'e', l => 0, r => 0, }, r => { d => 'g', l => 0, r => 0, }, } }; </code> <p>And here's a solution in 92 chars, that puts the tree into a single hash, and searches using the hash: <code> sub f{r(pop);$a{(pop)}||0;sub r{my$n=shift||return;$a{$n->{d}}=$n;r($n->{l});r($n->{r});};}; </code> <p>Speak up if I missed something. 73900 73900