// linked adjacency list representation of a directed graph
// initial version

#ifndef LinkedDigraph_
#define LinkedDigraph_

#include "lbase2.h"
#include "xcept.h"

class LinkedDigraph : public LinkedBase<int> {
   public:
      LinkedDigraph(int Vertices = 10)
        : LinkedBase<int> (Vertices) {}
      bool Exist(int i, int j) const;
      LinkedDigraph& Add(int i, int j);
      LinkedDigraph& Delete(int i, int j);
      int InDegree(int i) const;
   protected:
      LinkedDigraph& AddNoCheck(int i, int j);
};

bool LinkedDigraph::Exist(int i, int j) const
{// Is edge (i,j) present?
   if (i < 1 || i > n) throw OutOfBounds();
   return (h[i].Search(j)) ? true : false;
}

LinkedDigraph& LinkedDigraph::Add(int i, int j)
{// Add edge (i,j) to the graph.
   if (i < 1 || j < 1 || i > n || j > n || i == j
       || Exist(i, j)) throw BadInput();
   return AddNoCheck(i, j);
}

LinkedDigraph& LinkedDigraph::AddNoCheck(int i, int j)
{// Add edge but do not check for errors.
   h[i].Insert(0,j); // add j to vertex i list
   e++;
   return *this;
}

LinkedDigraph& LinkedDigraph::Delete(int i, int j)
{// Delete edge (i,j).
   if (i < 1 || i > n) throw OutOfBounds();
   h[i].Delete(j);
   e--;
   return *this;
}

int LinkedDigraph::InDegree(int i) const
{// Return indegree of vertex i.
   if (i < 1 || i > n) throw OutOfBounds();
   // count in edges at vertex i
   int sum = 0;
   for (int j = 1; j <= n; j++)
      if (h[j].Search(i)) sum++;
   return sum;
}

#endif