Graph.java

/** 
 * Defines the Graph class.
 */

package graph;
import java.util.ArrayList;
import java.util.HashMap;


// Graph class.
public class Graph {
	int[][] adjList;

  // Hash table to store nodes by index. 
  public HashMap<Integer, Node> nodesByIndex = new HashMap<Integer, Node>();


  /**
   * Constructor, assigning parameters to class properties and keeping
   * a HashMap of all nodes.
   * @param adjList Adjustment list: two params for no edge weights,
   * three params for edges with weight.
   */
  public Graph(int[][] adjList) {
    this.adjList = adjList;
    for (int[] edge : adjList) {
      Node from = nodesByIndex.get(edge[0]);
      if (from == null) {
        from = addNodeWithIndex(edge[0]);
      }
      int toIndex = edge[1], cost = 0;
      if (edge.length == 3) {
        toIndex = edge[2];
        cost = edge[1];
      }
      Node to = nodesByIndex.get(toIndex);
      if (to == null) {
        to = addNodeWithIndex(toIndex);
      }
      Edge e = new Edge(from, to, cost);
    }
  }

  
  /**
   * Creates and adds new node with a specified index.
   * @param index The index of the new node.
   * @return The added node.
   */
  public Node addNodeWithIndex(int index) {
    Node n = new Node(index);
    nodesByIndex.put(index, n);
    return n;
  }


  /**
   * Gets all neighbors indexex in an ArrayList.
   * @param index The index of the node to get neighbors from.
   * @return Array of all neighbor index or an empty array.
   */
  public ArrayList<Integer> getNeighborIndexes(int index) {
    ArrayList<Integer> result = new ArrayList<Integer>();
    Node a = nodesByIndex.get(index);
    if (a == null) {
      return result;
    }
    ArrayList<Node> arr = a.getNeighbors();
    for (Node n : arr) {
      result.add(n.index);
    }
    return result;
  }
}