This is the classis MAS mailmen problem where a set of mailmen
have to deliver a set of letters. Each letter must be delivered to
a different place and mailmen can exchange letters. The goal is to
minimize the total distance travelled by the mailmen. It is
an instance of a distributed resource allocation problem. The solution
provided here is only the most obvious. Better solutions are
possible. AFAIK, there is no agreement on what is the best
algorithm for solving this problem. This problem was first popularized in
Jose M Vidal
20100623