Re: Re: (Golf) Reversing RPN Notation

[MeowChow]

You have the right idea. Perhaps this will help you get started:

sub rpn_ptree {
  my@s;$o{$_}?$s[--$#s]=[$_,@s[-2,-1]]:push@s,$_ for@_;@s
}

It's a pretty well-golfed sub that builds a parse tree out of an RPN expression. The only tricky part is the --$#s, which simultaneously pops off the top element of @s (by assigning to $#s), and returns the index of the new end of the array. And here's another way to build a parse tree:

sub rpn_ptree {
  my$i;$o{$_[$i]}&&splice@_,$i-=2,3,[@_[$i..$i+2]]while++$i<@_;@_
}

   MeowChow                                   
               s aamecha.s a..a\u$&owag.print