Subtracting map iterators

Question

I have a program where I have two std::map iterators say left and right respectively. I want to find the number of elements in the ran

Answer 1

you can use policy based data structure which is compiler specific. More details can be found on this codeforces post The same can be used for set as well.

Answer 2

Is it possible to get an O(1) solution for this?

No. a std::map has a BidirectionalIterator. A BidirectionalIterator does not support random access and can only be incremented or decremented. That means if you want to move 5 positions forward you have to call ++iterator_name 5 times. If you need random access then you will need to pick a container that supports that like a std::array or std::vector.