Bloomberg Sr Software Engineer interview questions

It was very straightforward session. a leetcode medium level question. I found the algorithm very quickly because it was not new problem for me. I implemented with some mistakes but found and fixed all of them myself, after few test cases. after that he asked few design questions like how to protect the valid inputs, stuff like that. I answered all. it was quite positive and i believed i am going to next step. what happened? in just two days rejected! why? I am very sad now.