DFS

代码说明：

  深度优先搜索属于图算法的一种,英文缩写为DFS即Depth First Search.其过程简要来说是对每一个可能的分支路径深入到不能再深入为止,而且每个节点只能访问一次.(DFS Depth First Search is a kind of graph algorithm, English abbreviation for DFS is the Depth First Search. The process is briefly branch of every possible path can t go deep into the deep, and each node can only access at a time.)