Not OP but I did a 3 month boot camp, where the final month was spent on a big group project (which was great) and then algorithm optimization, red-black trees, and a bunch of stuff that I didn't actually think I needed on the job for 2 years.

Sometime in my third year on the job I had to find the duplicates in an array. My beautiful solution "arr.select{|x| arr.count(x) > 1}.uniq" didn't work because I had 100,000 items in the array. My solution was O(n^2), and that finally made sense to me, and it actually mattered.

I would say this was when I didn't feel like a Bootcamp beginner anymore, and thought of myself as an intermediate professional programmer.