I took an online test with 2 questions. I passed it, but at the time, they didn't have any available positions. They saved my details for the future, and indeed, one month later, I was invited for an interview day.

It included 3 online interviews, each lasting one hour and a half.

The day after the interviews, the recruiter called me and told me that I didn't pass, while describing the good things in the interview and the areas where I need to improve.

How to check if a string of different parentheses is valid or not.