Question

I’m developing an adjacency matrix so i can try and use a DFS to solve the euler circuit problem.
This is the relevant code to my question:

public class Graph {

private int numVertex;
private int numEdges;
private boolean[][] adj;

public Graph(int numVertex, int numEdges) {
    this.numVertex = numVertex;
    this.numEdges = numEdges;
    this.adj = new boolean[numVertex][numVertex];
}

public void addEdge(int start, int end){
    if(!adj[start][end])
        numEdges++;
    adj[start][end] = true;
    adj[end][start] = true;
}

When i try and test run this code by adding some edges i get:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 4
at Graph.addEdge(Graph.java:18)
at Graph.main(Graph.java:66)

I’m using this to test the code:

    public static void main(String[] args) {

    Scanner input = new Scanner(System.in);

    int numVertices = input.nextInt();
    int numLinks = input.nextInt();
    int startNode = input.nextInt();

    Graph g = new Graph(numVertices, numLinks);

    for(int i = 0; i<numLinks; i++){
        g.addEdge(input.nextInt(),input.nextInt());
    }

I think the problem is in the addEdge function. What am i doing wrong?

Answer 1

Remember that your matrix is zero-based.

If you passed 4 as numVertices, your matrix will go from 0,0 to 3,3.

Then if you try to add an edge between vertex 4 and any other you will have an error…