I think HackerRank is a great platform for challenges but I personally believe it only shows a small part of your skill set. I am a developer myself but also have hired a lot of engineers in my career. I believe that looking at existing projects you've done on Github gives a much better overview of your coding style, knowledge and your ability to learn. It also exposes some of the biases I know that we have in our own company (for instance, we know that if you have a functional programming background you'll fit in much better in our code base and team, even though we don't do functional programming).
All of this said, I think HackerRank is a great place to improve your skills in solving interview challenges and algorithmic problems.
Disclosure: I am a co-founder at source{d} where we analyse all git based projects to understand developers through their code.
From experience it's very hard to know how a candidate will perform when hired, irrespective of the hiring process.
A better recruiting model IMO would be to recruit people on short-term contracts (e.g. 6 months) with the contractual agreement that the worker will transition to a permanent job at the end of the 6 months providing their performance is inline with expectation.
I do use code exercises myself, but it's not some n queens problem or something - which tests nothing practical (for the positions in my team anyhow). Rather it's a simple problem, where I look for their ability to test drive code and clean code. The candidate then doesn't get pressured as they might in a live situation. If the code is good we walkthrough it in person.
"A better recruiting model IMO would be to recruit people on short-term contracts (e.g. 6 months) with the contractual agreement that the worker will transition to a permanent job at the end of the 6 months providing their performance is inline with expectation."
That already exists. And it leads to abuse of those contract workers, because they think that if they bust themselves just a little bit more, they'll have that carrot (the job). But they're so burnt out at the end of the contract period, and the employer inevitably says "No", and then brings in a new class of fresh faced hopefuls.
Your solution looks good on paper but if a candidate has two offers one permanent and the other the 6 month to permanent , I am pretty sure most would go for the permanent offer.
All of this said, I think HackerRank is a great place to improve your skills in solving interview challenges and algorithmic problems.
Disclosure: I am a co-founder at source{d} where we analyse all git based projects to understand developers through their code.