I indicated interest to multiple job ads on stackoverflow's job postings and had interviews with some of them. One company reviewed my CV and replied that that they want to move forward with the interview process, and for initial step they needed me to complete a test project through hackerrank. The project takes 3 days to complete (once you open the project 72 hour timer starts ticking). I spent three full says to do it. Submitted it. It wasn't some kind of major high end paying job and the company perhaps didn't have a good chance to hire me: by the time they reviewed my submission I have already received multiple offers, I had successful on-site interviews at google/facebook/snapchat/amazon/uber and multiple other smaller startups. So, after they reviewed my submission I received a simple reply "Unfortunately, we have decided not to proceed with your candidacy for the C++ Developer role". It was pretty shocking considering that I spent more than 24 hours to work on that project and all I got was an automated reply. I was like, C'mon, I spent 3 full working days doing your project and you cannot even provide feedback? I contacted them and got some feedback: first major point was completely bogus, they said it was inefficient :) My solution was efficient for sure, the other two reasons that they provided were about coding style that weren't completely wrong, but weren't real reasons in the scope of the project. I replied and explained that the performance issues that they mentioned were absolutely wrong, I also asked if my solution provided expected results, but I haven't got any replies after that. I assume solution was correct, otherwise they would obviously state that.
So, here's my point of the question: Should I send them invoice for three days of work that I've done on the project? While interviewing with all above mentioned companies I haven't spent more time on any of the interview processes for any single company than for this company with their 72-hour long project. I don't think it's reasonable to give people 72-hour long projects and then completely discard days of work after glimpsing them for 2 minutes. By the way, I may upload my solution to get second opinion from others.