// Directed graph implementation
public class Graph
{
  private int [][] adj;
  private String [] name;
  private int numVerticesPresent;
  private static final int MAX = 10;
  
  // Assume a maximum of 10 vertices.
  public Graph()
  {
    adj = new int [MAX][MAX];
    name = new String[MAX];
    numVerticesPresent = 0;
  }
  
  // copy constructor
  public Graph(Graph g)
  {
    adj = new int [MAX][MAX];
    name = new String[MAX];
    numVerticesPresent = g.numVerticesPresent;
    
    for (int i = 0; i < numVerticesPresent; ++i)
    {
      name[i] = g.name[i];
      for (int j = 0; j < numVerticesPresent; ++j)
        adj[i][j] = g.adj[i][j];
    }
  }
  
  public void addVertex(String s)
  {
    name[numVerticesPresent] = s;
    ++numVerticesPresent;
  }
  
  public void addEdge(String s1, String s2)
  {
    int i1 = findVertex(s1);
    int i2 = findVertex(s2);
    adj[i1][i2] = 1;
  }
  
  private int findVertex(String s)
  {
    for (int i = 0; i < numVerticesPresent; ++i)
      if (name[i].equals(s))
        return i;
        
    return -1;
  }
  
  // Go down the column and count the 1's.
  public int inDegree(String s)
  {
    int vertexNum = findVertex(s);
    int retVal = 0;
    for (int i = 0; i < numVerticesPresent; ++i)
      if (adj[i][vertexNum] > 0)
        ++retVal;
        
    return retVal;
  }
  public int inDegree(int vertexNum)
  {
    int retVal = 0;
    for (int i = 0; i < numVerticesPresent; ++i)
      if (adj[i][vertexNum] > 0)
        ++retVal;
        
    return retVal;
  }
  
  // Remove vertex as well as its out edges.
  // ADD CODE HERE
  public void removeVertex(int vertexNum)
  {
    
  }
  
  // Determine an appopriate toplogical ordering.
  // ADD CODE HERE.
  public void topOrdering()
  {

  }
}