Bloomberg Software Developer interview questions

It was phone screening and it was easy. Just basic knowledge of function, arrays and dictionaries. He asked me a tricky question about hast map which I got stucked on.

In the phone interview, I was asked to do graph related question and I chose c++ to solve it. In order to solve it, I used stl list with a pointer but I was told that this doesn't work, but I am %100 sure it is working, I tried to explain it but wasn't being listened, after that point I discouraged and then next day I got rejected.