This. After a couple years of serious effort on Codeforces, algorithms interviews are trivial. And perhaps more importantly, it becomes much easier to bang out

This. After a couple years of serious effort on Codeforces, algorithms interviews are trivial. And perhaps more importantly, it becomes much easier to bang out a state machine, toss around some data structures, check for edge cases. You'll become really comfortable with that middle tier of software algorithms that are a non-trivial composition of standard ideas, but still fall short of needing a research paper, etc. (And you'll develop a sense for when a problem is actually-hard).