FromWalesToJapan“I've been having real trouble with this exercise.”
Hmm. I can't imagine why. Assuming, as you did, that "present conditional" and "zero conditional" are equivalent:
Present / Zero: IF { present }, { present }
First: IF { present }, WILL ... ('LL)
Second: IF { past }, WOULD ... ('D)
Third: IF ... HAD {pp}, WOULD HAVE ...
All you need to look for is will, would, had, and would have. You don't even have to read and understand the other words in the sentences! What's so difficult about that? 
1. If I win the competition, I’ll share the prize money with you.
2. If you boil water, it turns into steam.
3. If the weather is nice tomorrow, I’ll go to the beach.
4. If only I had treated Yuki better, she wouldn’t have left me.
5. If you scratch my car, I’ll give you a smack.
6. If you touch the fire, you’ll get burned.
7. If you pay for me, I’ll go to the cinema with you.
8. If you save money now, you’ll have enough to travel to Spain next month.
9. If I could speak Spanish, I would be able to talk to people here in Spain.
10. If only I had learned to speak Spanish, I would have been able to order beer when I was in Spain last month.
11. If you come near my house again, I’ll kill you.
12. If you put your hand in the cage, the lion will bite you.
13. If you see Catherine, will you let me know?
14. If it rains, I’ll go to the cinema.
15. If I were you, I’d talk to your girlfriend about it.
16. If Martin comes in, will you give me a call?
17. If you are good to people, then people will be good to you in return.
18. If you don’t stop playing with my computer, you’ll break it.
Zero: 2.
First: 1., 3., 5., 6., 7., 8., 11., 12., 13., 14., 16., 17., 18.
Second: 9., 15.
Third: 4., 10.
CJ