How would you deal with this situation?

I have a friend who is super smart, I mean like crazy smart. I consider myself smart too, but nothing like my friend. We have this math cl together, in College, and it's not easy at all. I was very depressed once when I couldn't do well in some other cles that we took together. We had a test and I was actually proud of myself because I worked really hard, and during the test, there was one question where I couldn't get the answer but after some thinking, I got it, it was kind of a long answer but still, it was right. Right after the exam, I went to see my friend, very excited and told him about the problem, I told him the way I did it, but he said that I could have done it in a much simpler way. I believe him when he sys that because I know he's so smart and he's alway right, but, h told me that he hopes the professor would give me "some" credit for my answer, because, if it was him, he would give me zero! I was so shocked, I mean, my answer was right, it's just that I did it in a longer way. I mean, I certainly think I don't deserve "zero". After that, all my excitement fall down, I was actually happy and proud of myself and of my work for once, but then, I was really sad and I couldn't do anything much for the rest of the day. What do you think, am I overreacting? And if yes, how can I learn to deal with that kind of situation?