Good Array 1

**The definition of a good array coincides with Good Array $2$, but the other parts of the problem are different. Please read both statements carefully.** An array is called *good* if there exists some element $x$ such that $x$ appears **exactly once** in the array. For example, $[1, 2, 1]$ and $[1, 1, 2]$ are good because $2$ appears exactly once; but $[1, 2, 1, 2]$ is not. You call an array *b