I would say these questions are acceptable because I wouldn't like MSE to hinder a commendable studying attitude.
On the other hand, as OP commented on their question (I presume in response to the now-deleted question why they hadn't looked at other threads):
I was left in a weird position when I needed only hints and not full solutions, if I looked in other questions I was likely to ruin it.
meaning that any such "Hints only" thread is basically for the asker only -- anyone else wouldn't want to risk seeing the full solution.
Therefore, the future value of having this duplicate on the site is basically zero. So my suggestion is as follows:
Mark these questions as duplicates once one of the following takes place:
- OP accepts an answer;
- OP comments to answers in a thankful way;
- A reasonable amount of time has passed.
It seems to me that this approach could be the best of both worlds, although it requires some "maintenance work" to be done (the delayed closing of questions). I can imagine a meta-thread catering for this (if deemed necessary) as I perceive this type of hints-only-but-duplicate question to be relatively rare.