I applied through StackOverflow, and the hiring process went from May 2017 - June 2017. The first round was a 9-hour technical screening. Judging by the other interview reviews for this company, this was the same problem other candidates had. The requirements of the solution are stated very clearly in the problem statement. The solution shouldn't take more than 30 lines of code, and you shouldn't need to write conditions upon conditions for every corner case. You should test every corner case, yes, but a passing solution should handle them elegantly. The second and third rounds were Skype interviews with screensharing. You are permitted to use a text editor but not a compiler or debugger. I cannot share any details about the nature of the interview itself, but it seems like it uses the same problems as what other people have reported. You should be comfortable with writing a function that is mathematically rigorous, efficient, and elegant. Be prepared to "prove" that your program does what you want it to do. Treat the interview like a CS exam and take your time with finding the perfect solution! I was rejected after the third interview. HR told me that they could not disclose why my submission did not satisfy their expectations, but I was able to e-mail the interviewer and receive an explanation for one of the shortcomings of my solution. I understand that think-cell has high standards for code quality, but it would help to be more forgiving and less opaque with reviewing candidates' submissions.

After spending hours to do a test - they reject the application without even bothering providing feedback (and that despite the fact the test was well done and passing all the tests) - that is not a professional behavior and lacks respect for the time people invest in the process.