Click here to download CycleFinder.java.

public class CycleFinder {
  public static boolean hasCycle(Graph graph, String start) {
    // TODO you fill in this function
    return false;
  }

  public static void main(String[] args) {
    // XXX you shouldn't need to change anything here
    String dotf = Stdin.input("graph file: ");
    Graph graph = DotReader.readFrom(dotf);

    while (true) {
      String start = Stdin.input("starting node or 'quit': ");
      if (start == null || start.equals("quit")) break;
      if (hasCycle(graph, start))
        System.out.format("%s is in a cycle.\n", start);
      else
        System.out.format("%s is NOT in a cycle.\n", start);
    }
  }
}