HMMT 二月 2000 · ADV 赛 · 第 8 题
HMMT February 2000 — ADV Round — Problem 8
题目详情
- Ho w man y non-isomorphi graphs with 9 v erti es, with ea h v ertex onne ted to exa tly 6 other v erti es, are there? (Tw o graphs are isomorphi if one an relab el the v erti es of one graph to mak e all edges b e exa tly the same.)
解析
- It suÆ es to onsider the omplemen ts of the graphs, so w e are lo oking for graphs with 9 v erti es, where ea h v ertex is onne ted to 2 others. There are 4 di eren t graphs - see b elo w. 3 2