Picking the right data structure and algorithms gets your code in the right algorithmic complexity range - did you implement a naive linear algorithm, or did yo

Picking the right data structure and algorithms gets your code in the right algorithmic complexity range - did you implement a naive linear algorithm, or did you figure out a way to make it logarithmic? Or maybe even average-case constant? Compilers are generally not good at making optimizations that change complexity class. (Possible, yes, but not commonly.) That's not what jordigh is talking about. Let's say you figured out a clever way to get your problem to O(log n). That's definitely your job. But in practice, constants matter - that is, 10 log n is way, way worse in practice than 2 log n, even though they are both O(log n). And that's the kind of optimization that compilers may be better at than you. Once you have convinced yourself that the performance of some component matters, a good principle is to figure out the best complexity class you can (using the "right" data structures and algorithms), then write the most idiomatic code possible.