This could work for even occurences too. found = 1.

isn' the correct answer 1 here?

I love this.

Please use spoiler flag next time.

Thank you a lot, you helped me to understand the code above

This is some Dark Side Force here! =)

Thanks for the link.
See @Mr.Vine resplay. It fails on "new[] { 1, 2, 2, 3, 3, 3 }".

Very clever! Though it only works for odd occurrences (this would not work to find the one number with an even number of occurrences).

thanks for the explanations.