Strongly Connected Components

Given a directed graph, write a program that divides the graph into its strongly connected components.

A strongly connected component is a maximal set of vertices such that, for any two distinct vertices u and v in the set, there is a path from u to v and also a path from v to u.

A component may contain only one vertex. Such a single-vertex component does not require a self-loop.

The first line contains two integers V (1 <= V <= 10,000) and E (1 <= E <= 100,000), the number of vertices and edges in the graph.

Each of the next E lines contains two integers A and B, meaning there is a directed edge from vertex A to vertex B.

The vertices are numbered from 1 to V.

Print the number K of strongly connected components on the first line.

Then print K lines, one for each component. On each line, print the vertices in that component in increasing order, followed by -1 to mark the end of the line.

Print the components in increasing order of the smallest vertex contained in each component.