设在图G={V,E}中有一顶点r，Dijkstra算法可以求出其他所有点到点r的最短路径的跳数，这是求单源最短路径的一个最基本的算法。-There is a vertex, r, in the graph G={V,E}. As to every other vertex v, there exist several paths between v and r. The Dijkstra algorithm can get the hop count of the shortest path among those between v and r.