OYO Software Developer interview questions

My first round went brilliant, the interviewer asked me 4 coding questions, I gave all answers correctly. As soon as I finished my first round, I got a call on the phone for the second round directly. (Still, many people were waiting for the first round) My interviewer had a brilliant image of me, and he gave me like the most difficult graph and string problem, which I couldn't solve. So I got rejected. I was a deserving candidate, and the people whom they took were the people I used to teach. Great decision OYO!!