Submit says it should return 0 if B == 0. I guess your not allowed to take the difference between an array element and itself! By “pair” they mean 2 different numbers, not the same number twice.
By pair, it means 2 different positions, not two different numbers. For example, if you have your array as 3 1 3 and diff as 0, then 3 at index 0 and 3 at index 2 will form a pair.