Hi, all

I have a problem wich may solved greedily.

Background: Here is a group G of a people, one maybe another's friend. How to select least number of people to be a leader of a subgroup, so that everyone in the group G has a friend as a leader?

Translate: find least number of radial-subgraph of a graph. By radial-subgraph, it means a subgraph which has at least one point which connects all the other point in the subgraph.

Thanks!