IOI style means: partial scores, as many submisions as you want and it doesn't count the time when you submit or your number of submisions, everything that matters is your sum of your final scores of every problem. In these kind of contests you must firstly read all the problem and start with the easiest problems for you. If you don't know or you can not find a solution that gives you full score, you should make the brute force implementation and then make some optimizations. If you are a beginer, it's safe to do for all the brute force implementation, because you will have surely some points in your bucket with these, after that try to find better solutions.

I have tried two staregies on the IOI: 1-Spend an hour for each problem and try to score as much as you can, then sort the problems in order of expected difficulty and try to solve them for full scores. 2-Read all problems and work on getting full scores in order of excpected difficulty. Also, leave some time at the end for the easy points.

Both worked for me during practice. However, I am not sure if they are good as I did very bad in both IOIs which I have been to.

In 2016: I used the 1st strategy on both days. The reason why I did bad: I tested my solution for the 1st problem with a WRONG test case, and thought that my solution was incorrect. Alongside, missing few easy points on the second day.

In 2017: I used the 2nd startegy on the first day, and the 1st one on the second day. The reason why I did bad: I spent most of my time on one problem (didn't solve it at the end) and when I wanted to code the easy points, which were about 130 points, I was very stressed and only got 23 LOL. That is why I went back to the first strategy on the second day which is safer.

To summurize, in both years I missed more than 100 points, missing the chance to get a silver medal two times. But, I think that was due to stress and careless mistakes.

Back to your question, I think the first strategy is safer. However, you must try different strategies of your own and the find the one then suits you best. Good luck!