This is a very efficient and creative solution; that said it sacrifices some readibility for that efficiency.

the nums[1:] in range will create a new slice without first element, and we compare "v" with arr[i] (previous element of slice nums)

All numbers are equal except for one.

[0.2, 1.2, 1.4, 1, 1.2, 10, 1.4, 124]

this function work not correctly

It would fail. In my case (and I suppose not only mine) there was an array with 5 different numbers and only one of them was unique.

I know the test cases don't cover it, but what if at least one of them was 0? ;-)

Mine is exactly same as yours, (each line and each word) :P :P

Well, returning 2.0 isn't really an error. The description didn't define the behavior for invalid inputs. From the description, "There is an array with some numbers. All numbers are equal except for one." Your list doesn't match the expectations for this kata, so I'm not sure what you expected to be returned.

When [1.0,1.0,1.0,2.0,2.0,3.0] result is errors

for i, v := range arr[1:] to skip a few elements in the array

Slick, also the most efficient. Well Done.

🤔

Not an issue.