NuTonomy interview question

How to deal with class imbalance in a machine learning problem? How do you evaluate an object detection algorithm? Tell me some examples about two stage and single stage object detection algorithm. How about 3D object detection? Tell me some examples about segmantic segmentation, and instance segmentation method. One leetcode medium question (just explain possible solution). What's the worst case of searching from a hash map? How do you check GPU memory usage on Linux?