Minimum Spanning Tree: Prim. Kruskal.
Strongly connected: A directed graph is called strongly connected if there is a path from each vertex in the graph to every other vertex.
mathematician-language problem friends problem
一次会议有 n 名教授 $A_1, ..., A_n$ 参加，证明可以将这 n 个人分为两组，使得每一个人 $A_i$ 在另一组中认识的人数 $d_i$ 不少于他在同一组中认识的人数 $d_{i}^'.
Last Modified: October 22, 2011 22:18:35