My honest opinion from studying math for a while as a non-mathematician: getting to an advanced level in combinatorics and algorithms is simply way less difficu

My honest opinion from studying math for a while as a non-mathematician: getting to an advanced level in combinatorics and algorithms is simply way less difficult than getting to an advanced level in say, analytic number theory. Get some combinatorics textbooks and just grind through all the exercises. Grind TAOCP. Do this for 12-24 months diligently and you can legitimately become an expert. (If it seems unpalatable to have to do this simply to get a data science job, then I certainly sympathize)