sub f{for(($s,$t)=@_;$_=$$t{(0,l,r)[$$t{d}cmp$s]};$t=$_){}$t}

##</code><code>##

sub f{for(($s,$t)=@_;$_=$t&&(0,l,r)[$$t{d}cmp$s];){$t=$$t{$_}||0}$t}

##</code><code>##

sub f{for(($s,$t)=@_;$_=$t&&(0,l,r)[$$t{d}cmp$s];){$t=$$t{$_}}$t}

##</code><code>##

    $|++;
    $table = {
        d => 'h',
        l => {
             d => 'd',
             l => { d => 'b', l => { d => 'a' }, r => { d => 'c' } },
             r => { d => 'f', l => { d => 'e' }, r => { d => 'g' } },
        },
        r => {
             d => 'l',
             l => { d => 'j', l => { d => 'i' }, r => { d => 'k' } },
             r => { d => 'm', l => { d => 'l' }, r => { d => 'n' } },
        }
    };

    foreach $y (qw[ a b c d e f g h i j k l m n o p q ])
    {
            $x = f($y,$table);
            print "Answer for $y = ";
            print $x," ", $$x{d},"\n";
    }