[vicaya]

I'd expect better write up from Daniel. std::unordered_set is implemented with chained buckets, which incurs extra memory references. Cursory google revealed that an open addressing hash set would be about 3x faster, which would handily beat the sort version.

[rurban]

This, and the sort solution is also incredibly bad. The third unique step does unnecessary moving of all the remaining values. Multiple times. You just need to iterate over the sorted array and skip i++ when the value is the same as the previous.