The main issue here is how to sort out the usage of "the" with "least". Sometimes it's clear but there are cases when I am not sure whether to use the article "the" or not.
Least with verb
- The man who actually won the car is the one who wanted it least. [No “the”.]
- The President seemed to be the one who knew least about the crisis. [No “the”.]
(The sample sentences are from a dictionary.)
- I earn the least out of all of us. [Again from a dictionary.]
- Which subject do you like the least? [Found randomly on the Internet.]
I have come to a vague idea which can explain it to some extent. For example: I earn the least out of all of us. = I earn the least (amount of money) out of all of us. So, when “the” is used it adds an idea of substantivisation i.e. “the least” is a noun.
However, it seems like there are cases when my explanation doesn’t work. E.g., "Which subject do you like the least?" I don’t see how it can be interpreted as a noun. I think it should be "Which subject do you like least?"
Least with participle
- I'm not the least surprised that she's leaving. [Taken from a dictionary.]
- The reply will discuss the one you are least interested in. [Found randomly on the Internet.]
I think it should be: "The reply will discuss the one you are the least interested in."
I am not sure if my ideas are correct, I am just making them known to you so that you can understand the way I think in respect to the issue and shed some light on the issue.