loanDepot Software Engineer interview questions

I applied online, and their senior corporate IT recruiter contacted me back and had a phone interview. He asked me a few technical questions about C#, like about an access modifier, inheriting from class or interfaces, and big O notation for hashtable. Then had second phone interview, with a senior software engineer. He went through an interactive scenario, about troubleshooting the slow response time for a ZIP code validator. It was a neat exercise to explain my thoughts, but he didn't seem satisfied with my response about implementing it in C# instead of the database. Maybe he preferred more concrete detail, to which I would have suggested using a sorted dictionary and LINQ or search algorithm. I got a called back the next business day from the corporate recruiter saying I wasn't strong enough in the technical exercise. I never made it to the onsite interview(s). They were nice and tried to be helpful on the phone, which I appreciate.