Imagine you are responsible for leading a car rental company. You are given a collection of reservation times with the following structure:

struct reservation{
	int id;
	int pickup_time;
	int return_time;
}

Your task is to assing as less cars as possible to the collection of reservations. 
Furthermore, you are tasked with returning the set of time intervals each respective car was used.

Example Input:
Reservations: [[1,4],[2,5],[3,7],[6,9]]

Example Output:
car1 -> [{1,4},{6,9}]
car2 -> [{2,5}]
car3 -> [{3,7}]

Constraints and questions, which I asked:
	- Is the collection of reservations sorted? -> No
	- Are there any rules according to which the available cars should be assigned? -> No, just pick any arbitrary car, which is available