How to select a random element in std::set in less than O(n) time?

Question

This question with an added constraint.

I\'m willing to allow not-uniform selection as long as it\'s not to lop sided.

Given that \"sets are typically imple

Answer 1

For std::unordered_set s:

1) take random R in min(s)..max(s)

2) if R in s: return R

3)

newIter = s.insert(R).first;
newIter++;
if (newIter == s.end()) {
    newIter = s.begin();
}
auto result = *newIter;
s.erase(R);
return result;

For ordered set (std::set) probability would depend on distance between elements. unordered_set is randomized by hash.

I hope this can help.

PS converting std::set into std::set> (where first element in pair is a hash of second) makes this method suitable for any hashable V.