Problem 2561. expand intervals vol.3

This is the next problem after 2528 and 2560. It is a more general case, when bounds creates intersections between intervals. Description changes as follow:

Given a row vector of an even number of scalars. Each pair create bounds of an interval but their occurence may vary. Return a row vector which consists of all the integers, ordered, non repeated, within these intervals (union of integer intervals).

See also problem 1986