DevRev Software Internship interview questions

Coding round - 4 questions were asked 2 were basic string questions. One was printing all subsequence sum with repeated elements One was snake and ladder dp question I solved all 4 and was selected for interview, among 22 students. Round 1- the interviewer was very friendly and started off by asking about my projects. I had prepared well so i was able to answer everything. Next he asked me 3 technical questions- Subarray sum 0 3sum problem Climbing stairs using one or two steps dp I answered everything and was selected for round two, among 5 students. Round two- the interviewer asked me about all my projects nd checked if they were genuine. Then he asked me a question based on version stack. We were required to make a stack where every push or pop operation resulted in a new version of the stack, and a set-version function to restore the particular version of stack. Pop function required us to print the version and the deleted elements. All operations were to be done in O(1). I wasnt able to completely solve and the interviewer seemed dissatisfied. I was rejected, and 3 students got offers.