#ifndef _GRAPH_H
#define _GRAPH_H

#include <iostream>

#include "Digraph.h"

// undirected graph
//
// restriction: at most one edge between any pair of vertices

// we implement the graph G=(V,E)
//  using the directed graph D=(V,E')
//  where E' = { (i,j) : {i,j} in E and i <= j }
// 

class Graph {
 private:

  Digraph D;

  void sort(int& i, int& j) const {  if (i > j) {  int t = i;  i = j;  j = t;   } }

 public:

  ~Graph() {};			// destructor

  Graph() {};			// constructor
  Graph(const Graph & g) : D(g.D) {} // copy constructor

  int add_vertex() {	     // adds vertex, returns non-zero integer id for vertex
    return D.add_vertex();
  }
  int add_vertex(int id) {    // adds vertex using given id (if not already there)
    return D.add_vertex(id);
  }
  void add_edge(int from, int to) { // adds edge, vertices from and to must already exist
    sort(from, to);
    D.add_edge(from, to);
  }
  int edge_exists(int from, int to) const { // return whether exists edge from "from" to "to"
    sort(from, to);
    return D.edge_exists(from, to);
  }
  int vertex_exists(int v) const { // is there a vertex with id v
    return D.vertex_exists(v);
  }
  
  void remove_vertex(int v) {	     // remove any vertex with id v
    D.remove_vertex(v);
  }
  void remove_edge(int from, int to) { // remove edge between "from" and "to"
    sort(from, to);
    D.remove_edge(from, to);
  }

  Array<int> vertices() const {	// return array of vertex ids in graph
    return D.vertices();
  }

  Array<int> nbrs(int v) const { // return array of ids of neighbors
    Array<int> in = D.in_nbrs(v);
    Array<int> out = D.out_nbrs(v);
    for (int i = 0;  i < out.size();  ++i) {
      in[in.size()] = out[i];
    }
    return in;
  }

  void clear() {	   // make graph empty (no vertices, no edges)
    D.clear();
  }

  Graph& operator=(const Graph& g) { // assignment operator
    D = g.D;
  }

  friend std::ostream& operator<<(std::ostream& out, const Graph & g);

};

std::ostream& operator<<(std::ostream& out, const Graph & g) {
  out << g.D;
}

#endif