If this is referring to codility, don't worry. Codility is extremely poor at writing its requirements for the problem it wants you to solve. They're extremely t

If this is referring to codility, don't worry. Codility is extremely poor at writing its requirements for the problem it wants you to solve. They're extremely technical requirements, and there is no one to direct your questions to. I was interviewing for a company that did that and I thought the exact same thing. I consistently received failing grades with little to no explanation, the tests weren't descriptive. I chalk it up to codility sucks. Don't get down on yourself. one of the problems, the ONLY solution is a bitwise XOR for num in nums: var a ^= num kind of thing. That is the ONLY answer. But they don't clearly describe the optimization they're looking for in that problem either. In my opinion, the only way one could have known how to solve this is if they already knew about bitwise operands at a deep level. Which 99% of all code ever written will never use. In other words, I don' think it's any kind of commentary on your skills, but rather poor questioning, and structure of codility, if we're talking about codility, which I think we are.