I was confused about the submission file.
If pair (u, v) is a correct user_id pair, of course the pair (v, u) also is a good pair.
So, I need to write both of them in submisson.txt or I just need to write one of them?
If I just need to write one of them, which one? alphabet order? random one?
> If I just need to write one of them, which one? alphabet order?
Yes, you should write it once in alphabet order.
For example, if your model predict that (de11faee75df4d788b507d9dcb992b78, 55445afef0c745acad49b2866bcb5464) is correct pair, you should write
"55445afef0c745acad49b2866bcb5464,de11faee75df4d788b507d9dcb992b78" in your submission.