偶图的周长

Circumference of bipartite graph

设Ｇ是以（Ａ，Ｂ）为顶点二分划的偶图，ｄ（ｘ）＝ｍｉｎ｛ｄ（ｕ）｜ｎＡ｝＝ｋ≥２，λ＝ｍｉｎ｛ｄ（ｕ）｜ｕＡ＼（ｘ）｝≥ｋ，２≤｜Ａ｜≤λ，｜Ｂ｜≤λ＋ｋ－２，则Ｇ的周长为２｜Ａ｜．

If G is a bipartite graph with bipartition (A, B),d (x )= min {d (u) | u A }= k≥2, λ={d(u) |n A\{x} }≥k,2≤| A | ≤λ, |B|≤λ+k-2,then C(G) = 2 |A |.