My experience over about 20 years of writing software professionally is that I need to tackle one algorithmic problem a year. Probably amounts to a day or two

My experience over about 20 years of writing software professionally is that I need to tackle one algorithmic problem a year. Probably amounts to a day or two of work, and usually it is a refinement or adaptation of an existing algorithm, rather than totally new code. Call it less than 1% of my time.