A graph is a set of vertices and a collection of edges that each connect a pair of vertices. We use the names 0 through V-1 for the vertices in a V-vertex graph.
图是由一组顶点(vertex)和一组能够将两个顶点相连的边(edge)组成的。
特殊的图：
A self-loop is an edge that connects a vertex to itself.
自环, 即一条连接一个顶点和其自身的边。
Two edges are parallel if they connect the same pair of vertices.
连接同一对顶点的两条边成为平行边。
When an edge connects two vertices, we say that the vertices are adjacent to one another and that the edge is incident on both vertices.
当一条边连接两个点，我们就说这个两个点互相邻接，邻接点
The degree of a vertex is the number of edges incident on it.
图中边的个数叫做度。
A subgraph is a subset of a graph's edges (and associated vertices) that constitutes a graph.
由图的点和相应的边的子集组成的图叫子图。
A path in a graph is a sequence of vertices connected by edges. A simple path is one with no repeated vertices.
路径是由边顺序连接的一系列的点。 简单路径是一条没有重复顶点的路径。