Question

I use a std::set to sort a vector of unordered duplicate values. Every time I find an element in my set, I need to know the position (index) of the element as well. There are a lot of elements (hundreds of thousands) in my set, and using std::distance() gives me abysmal performance.

Is std::distance the only way to go?

Answer 1

You can sort the elements in place using the std::sort() algorithm. Then when you find an element in the vector using binary_search() just subtract the result of a call to begin() from the iterator pointing to the element.

Another alternative is to use std::partial_sort_copy() if you don’t want to overwrite your original vector. Just sort into another vector and you can do the same thing I described above.