When answering one coding question, I gave the solution in C++ by utilizing the STL. However, the interviewer didn't know C++/STL very much. When I gave the complexity analysis, he was definitely not satisfied because I involved some details on the STL container (HashMap). I told him that mapping in HashMap in C++ 10 isn't constant time complexity and he felt confused and asked me to implement one hashtable that does have constant time complexity. Somehow, the interviewer couldn't be satisfied anyway. And this was really frustrated.