Computes a vertex cover in an undirected graph. A vertex cover of a graph is a set of vertices
such that each edge of the graph is incident to at least one vertex in the set. A minimum vertex
cover is a vertex cover having the smallest possible number of vertices for a given graph. The
size of a minimum vertex cover of a graph G is known as the vertex cover number. A vertex cover
of minimum weight is a vertex cover where the sum of weights assigned to the individual vertices
in the cover has been minimized. The minimum vertex cover problem is a special case of the
minimum weighted vertex cover problem where all vertices have equal weight.