NVIDIA Software Engineer interview questions

Phone interview, talked about the position (cuda kernels for deep learning) and 2 coding problems. Very friendly. I was unprepared for technical interviews at the time unfortunately. Overall the interviewer was very professional, never once hinted that he was impatient due to my lack of preparation and answered all my questions very thoroughly.

a few questions were asked. very nice and inviting nice nice interviewer nice workplace given n pairs of numbers and one extra number in an array (size of array is 2n + 1) how can you know in O(n) with one iteration over the array which number did not come in pair