It seems this kata actually requires finding those prime factors which is a (very) hard problem in general. I'm not sure whether non-sophisticated approaches will work here (that depends on the size of the input numbers), so I will skip this kata for now.

Great stuff, love it! Contains some nice hidden details such as using operator< on std::pair<>, C++14 lambda captures with initializer, etc. that make the solution very dense.

Greatest drawback, in my opinion, is that it doesn't work for empty lists of intervals where it does invoke UB (because of intervals[0]). I fixed that in a fork, and additionally improved readability a bit more by using some other modern C++ features.

This kata has been much more fun than I initially thought it would!

Dope!

Lol

I wouldn't want the (unnecessary) memory consumption of the intermediate ranges vector in this solution. Imagine millions of ranges the size of 1 or 2...

When the integer list args is empty on input, wouldn't you then get an empty result string, call pop_back() on an empty string thereby triggering Undefined Behaviour?

Slow but nice and simple.

And after that, try to do it with only one single pass over the input! That is, look at each character only once. ;-)

enumerate() returns a special generator from an iterable. In itself, it has O(1) runtime and does not split anything. If anything it is the iterator of str that is "splitting" (or better: iterating) the string into individual characters if you mean that. enumerate() just adds indices on top of that.