Yes, and even a simple string like "...---..." has 200 possible solutions, including "VTTIE", "3NI", and "SMB". Especially for longer inputs, there's no way to guess which one is right.

SOS is an interesting case, because it is a Morse "prosign", which means it is sent as one continuous stream of dits and dahs without any pauses between the letters we use to represent it.

In other words, SOS is sent exactly the way you wrote it, as if it were one long character:

  ...---...

It is not sent as three separate letters like this:

  ...  ---  ...

To indicate this special treatment, prosigns are normally typeset with a bar over the connected letters, something like this:

  ___
  SOS

(I used underscores above the letters here; if they render as separate underscores, imagine that they all run together.)

They inserted spaces though, between characters and words. In this problem, all spaces are removed.

We also have to do that to decode speech. You can simulate the way people do it with a hidden Markov model.

That's a prefix code, they're defined by no code word being a prefix of another (so if you put them in a trie the code words only appear on leaves).

A trivial example is the reverse:

  _.
  _..
  _...

Which can be decoded by, at worst, reversing the string first.

(Sorry if I've misunderstood your example)