Slack Software Engineer Analytics Infrastructure interview questions

They are quick to respond and give feedback. Overall, I feel like the recruiting team is great but I feel interviewing with this company is a waste of time. They are very vague about what they are looking for in candidate. The coding problem they give is very vague and they don't specify what exactly they are looking for. I have feeling that they have preselected candidate. I wasn't given any feedback as to why I was rejected. Or they probably want an ivy league candidate like all other Silicon Valley companies. I don't even know why they bothering wasting other people's time if you don't want to provide feedback or have a candidate in mind.