Amazon SDE-intern interview questions

The interviewer asked two medium level DSA questions. First it started with my introduction and he asked to tell about the recent project i have worked on. The he gave me two dsa questions which i solved, but i was not able to convey the logic of second question.

First round was Online Test with 2 questions in 1 hour followed by interview 1 hour 2 questions the questions in OA was 1 medium and 1 difficult. I solved both questions than moved to interview round