agree ;)

@JChampt in my opinion, sorting is a bottleneck in your solution

Clever. I didn't think about using hash table for keeping both indexes and watching for a duplicate. I used a Set for the latter.

That's true, but people still seem to like it ;-)

It works, why don't you test it?

I think this only works if the unique number is one of the first three numbers of the array.
In case of arr=[1,1,1,1,1,2], then arr[:3] is [1,1,1] and the unique is not in it.

<3

Omg never thought of that! You just made this solution so much better, that means we will only iterate through this once!