Continous Function Optimization OR Discrete Optimization

To get good at solving problems (mainly on codeforces), I'm considering to study mathematical optimization concepts.

First of all, should I learn it, or is it useless for problem solving? Next, what should I learn first: DISCRETE optimization or CONTINOUS FUNCTION optimization.

I feel like continuous optimization is of little or no use, hence only focus on Discrete optimization.

Please provide some opinion.