Can you give me a hint? What is the complexity? The
solution is O(n^2) with heuristics?

The best solution is O(n).
Note that there is always an answer of the kind x and x+1.
And don't forget to take care of overflows.

> Can you give me a hint? What is the complexity? The
> solution is O(n^2) with heuristics?

Thank you very much