I was asked to write a program to find common items between 2 lists.I used java to write the program. I wrote the program which was iterating the smaller array list and used contains. The Hiring manager argues with me saying that the code is not efficient enough because 'contains' method on arraylist would lead to o(n) and that would result in O(m*N)(which is incorrect) In the interview, I was not able to google it and I was taken aback when he was talking so assertively as I assumed that he understands java. However, after I hung up the phone I realized that I am indeed right and that the algorithm I created was very efficient. The interviewer came to the interview with a view to reject me. Its a waste of time. They should let subject mattter experts do the interviews, not the people with background in c/C++ interview java guys or the other way round. The hiring manager seemed very professorial background. I tried to tell recruiter to let them know the problem, but I do not think even she has any clue on how to approach.