图的遍历

代码说明：

  基本要求：以邻接表为存储结构，实现连通无向图的深度优先和广度优先遍历。以用户指定的结点为起点，分别输出每种遍历下的结点访问序列和相应生成树的边集。(Basic requirements: the adjacency list is used as storage structure to realize the depth first and breadth first traversal of connected undirected graph. Starting from user specified nodes, we output each node access sequence and the corresponding edge set of corresponding spanning tree respectively.)