On 7/19/06, Yohanes Santoso <ysantoso-rubytalk / dessyku.is-a-geek.org> wrote:
> "David Balmain" <dbalmain.ml / gmail.com> writes:
>
> > On 7/19/06, Yohanes Santoso <ysantoso-rubytalk / dessyku.is-a-geek.org> wrote:
> >> "David Balmain" <dbalmain.ml / gmail.com> writes:
> >>
> >> > Hey all,
> >> >
> >> > I need to come up with a way to encode an integer as a string so that
> >> > it will sort correctly lexicographically. This is pretty easy when you
> >> > have a fixed integer range but how do you do it with Ruby's BigNums?
> >> > Any ideas?
> >> >
> >> > Cheers,
> >> > Dave
> >>
> >> def encode_integer(num)
> >>   "x"*num
> >> end
> >>
> >> Do I win something?
> >>
> >> YS.
> >
> > Nice idea :P
> > But how about negative numbers.
>
> Same technique, but put them in different namespace.
>
> YS.

I need to be able to compare positive integers with negative so I
would need to add a bit to this technique, (not to mention a couple of
terabytes of memory to handle even moderately large numbers :))

def encode_integer(int)
  if (int > 0)
    "z" * int
  else
    "x" * -int + "y"
  end
end

Anyway, here is a better solution using only only digits 0-9. I'll
extend it myself to use the full ascii alphabet;

def encode_int(int)
  if (int > 0)
    int_str = int.to_s
    ("3%04d" % int_str.size) + int_str
  elsif (int < 0)
    int_str = (-int).to_s
    ("1%04d" % (9999 - int_str.size)) + (10 ** (int_str.size + 1) + int).to_s
  else
    "2"
  end
end

Cheers,
Dave