二分图是一个无向图，它的n 个顶点可二分为集合A和集合B，且同一集合中的任意两个顶点在图中无边相连（即任何一条边都是一个顶点在集合A中，另一个在集合B中）。当且仅当B中的每个顶点至少与A中一个顶点相连时，A的一个子集A 覆盖集合B（或简单地说，A 是一个覆盖）。覆盖A 的大小即为A 中的顶点数目。当且仅当A 是覆盖B的子集中最小的时，A 为最小覆盖。-two hours map is an undirected graph, it n vertices can be divided into two pools A and B pools. but the same set of arbitrary vertex of the two map linked to the billboard (that is, any one side is a culmination of the pool A, in another pool B). If and only if each of the B vertex with at least one vertex A connected, A subset of a pool A B coverage (or simple to say that A is a cover). A coverage of the size shall A number of vertices. If and only if A is a subset B coverage focus on the smallest, A for minimum coverage.