// Stephanie's class notes.
// sorely missing comments and docstrings. sorry.
// Graph implemented with adjacency matrix
// Note: I have implemented the graph as a digraph. If you want to connection
// node A to node B, it puts in an edge from A to B, but not the corresponding
// edge from B to A.
import java.util.*;
public class Graph4 {
    private int[][] edges;
    private GraphNode[] nodes;
    
    public static class GraphNode {
        String label;
        
        public GraphNode() {
            this.label = "";
        }
        
        public GraphNode(String label) {
            this.label = label;
        }
                
        public String toString() { 
            return this.label;
        } 
    } // end class GraphNode
    
    // I have the constructor make all the nodes, too. 
    // Depending on how you want to use this class, that could have
    // been a terrible decision.
    public Graph4(int numNodes) {
        this.nodes = new GraphNode[numNodes];
        for (int i = 0; i < numNodes; i++)
            this.nodes[i] = new GraphNode( "n" + Integer.toString(i) );
        this.edges = new int[numNodes][numNodes];
    }
    
    public void connect( int fromNode, int toNode ) {
        this.edges[fromNode][toNode] = 1;
    }
    
    public void printAll() {
        for (int fromIdx=0; fromIdx < this.edges.length; fromIdx++) {
            GraphNode n = this.nodes[fromIdx];
            System.out.print( n  + ": ");
            for (int toIdx = 0; toIdx < this.edges.length; toIdx++) {
                if (this.edges[fromIdx][toIdx] > 0)
                    System.out.print( this.nodes[toIdx] + " " );
            }
            System.out.println();
        }
    }
    
    public static void main( String[] args ) {
        Graph4 g = new Graph4(3);
        g.connect( 0, 1 );
        g.connect( 2, 1 );
        g.printAll();
    }
}