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Simple datastructures and algorithms.

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/* $Id: Graph.java 312 2006-07-03 22:20:47Z sam $ */

package com.github.basking2.sdsai.sandbox.graph;
import com.github.basking2.sdsai.Key;
import com.github.basking2.sdsai.Set;

/**
 * This is a wrapper class for working with nodes.
 * The Graph class takes much of the complexity out of dealing
 * with node and edge objects but at the cost of time.
 * The Graph class seeks to enforce definitions of a Graph.  Those being
 * that no node can be in a graph twice.  No edge can exist twice.
 * There is no edges from a node to itself and there is no more than 
 * one edge in a given direction from one node too another.
 * Note that while the Graph class tries for correctness, the users has
 * many opertunities to break that correctness.
 */
public class Graph 
{
  Set nodes;
  Set edges;

  public Graph(){ nodes = new Set(); edges = new Set(); }
  
  /**
   * Add and edge from start to stop.
   * If an edge already exists between start and stop that edge is returned.
   * Other wise, the new edge created from start to stop is created.
   */
  public Edge addEdge(Node start, Node stop)
  {
    Key nodekey;

    /* If we don't already have these nodes, add them. */
    nodekey = new Key(start.hashCode(), start);

    if( ! nodes.member( nodekey ) )  nodes.add(nodekey);

    nodekey = new Key(stop.hashCode(), stop);

    if( ! nodes.member( nodekey ) )  nodes.add(nodekey);

    /* Note: This works for undirected nodes too. */
    Edge e[] = start.getOutEdges();
    
    for(int i=0; i(tmpe.hashCode(), tmpe));

    return tmpe;
  }
}