Initializes an empty flow network with V vertices and 0 edges.

Initializes a flow network from an input stream. The format is the number of vertices V, followed by the number of edges E, followed by E pairs of vertices and edge capacities, with each entry separated by whitespace.

Initializes a random flow network with V vertices and E edges. The capacities are integers between 0 and 99 and the flow values are zero.