Pocket Gem OA: Path Finder

1. 有向图 找所有start node到end node之间的路径
    输入是一个txt 形式如下：
      A E
      A : B C D.
      B : C
      C : E
      D : B.
输出一个List<String> 是从A到E所有的path

题不难，主要是注意STDIN

 package pocketGems;

 import java.io.*;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Set;

 public class PathFinder2 {
     public static void main(String[] args)
             throws FileNotFoundException, IOException {
         String filename = "C:/Users/yang liu/workspace/Interview2017/src/pocketGems/input_1.txt";
         if (args.length > 0) {
             filename = args[0];
         }

         List<String> answer = parseFile(filename);
         System.out.println(answer);
     }

     static List<String> parseFile(String filename)
             throws FileNotFoundException, IOException {
         /*
          *  Don't modify this function
          */
         BufferedReader input = new BufferedReader(new FileReader(filename));
         List<String> allLines = new ArrayList<String>();
         String line;
         while ((line = input.readLine()) != null) {
             allLines.add(line);
         }
         input.close();

         return parseLines(allLines);
     }

     static List<String> parseLines(List<String> allLines) {
         HashMap<String, HashSet<String>> graph = new HashMap<String, HashSet<String>>();
         Set<String> visited = new HashSet<String>();
         String src = allLines.get(0).split(" ")[0];
         String dst = allLines.get(0).split(" ")[1];
         for (int i=1; i<allLines.size(); i++) {
             String line = allLines.get(i);
             String node = line.trim().split(":")[0].trim();
             String[] neibors = line.split(":")[1].trim().split(" ");
             graph.put(node, new HashSet<String>());
             for (String nb : neibors) {
                 if (nb.length() != 0) graph.get(node).add(nb);
             }
         }

         List<String> res = new ArrayList<String>();
         visited.add(src);
         helper(res, src, src, dst, visited, graph);
         return res;
     }

     static void helper(List<String> res, String path, String cur, String dst, Set<String> visited, HashMap<String, HashSet<String>> graph) {
         if (cur.equals(dst)) {
             res.add(path);
             return;
         }
         HashSet<String> neibors = graph.get(cur);
         if (neibors != null) {
             for (String each : neibors) {
                 if (visited.contains(each)) continue;
                 visited.add(each);
                 helper(res, path+each, each, dst, visited, graph);
                 visited.remove(each);
             }
         }
     }
 }