I don't think it matters that much. Before Leetcode there were books like Cracking the Code Interview. It's not like Google owns dynamic programming interview questions. Some companies with a similar hiring bar ask Leetcode questions verbatim. What matters is how you do it and what you expect from candidates.
Before that I remember talking about interview questions with others at college. Also joelonsoftware.com (from Joel Spolsky who later was a cofounder of Stackoverflow) had a sister site called techinterview.org and I'm sure there were other sites.
