I had a phone screen with them. The interviewer gave me a task, which I already knew the solution for at first: find two elements in an integer array which sum up to a given number.

When I pointed out that I knew the solution to the problem, he gave me another one: to determine if a sequence of numbers is monotonic (i.e., ascending or non-descending). The interviewer didn't seem to understand the difference between non-decreasing and ascending sequences, and it took a while to figure out the exact specification for the problem.

The interviewer expected a straightforward solution that compares elements pairwise, but I came up with a more elegant one, which is based on calculating the pairwise difference and would require only a single array traversal. The interviewer didn't understand my solution and told me that he hadn't seen this solution before and it wasn't the one he was expecting. Eventually, he couldn't come up with an example where my code wouldn't work or a flaw in my reasoning.

I received feedback that my solution wasn't the one the interviewer was expecting and was therefore rejected.

Determine if a sequence of numbers is monotonic.