giving travel time between any given pair of nodes.
This is an example of the classic traveling salesperson problem.
Formally, we are given a set of n nodes V (points, vertices,
cities, holes), and a distance function
giving travel time between any given pair of nodes.
We want to find a tour (Hamiltonian circuit, permutation)
of the nodes 
such that 
is minimized. It's the shortest trip
that visits every city once and only once.
We'll assume the distance function D is symmetric: D(u,v)=D(v,u) for all u and v in V.
In the metric TSP, we additionally assume that distances
obey the triangle inequality: for all u and v and w in
V, 
(shortcut is never worse).
