# Graph Data Structure

## Definition

Graph node for a *directed* graph

```java
class DirectedGraphNode {
    int label;
    List<DirectedGraphNode> neighbors;    
    GraphNode(int val) {
        label = val;
        neighbors = new ArrayList<DirectedGraphNode>();
    }
}
```

Graph node for an *undirected* graph

```java
class UndirectedGraphNode {
    int label;
    List<UndirectedGraphNode> neighbors;    
    GraphNode(int val) {
        label = val;
        neighbors = new ArrayList<UndirectedGraphNode>();
    }
}
```

We can use the same graph node for an *undirected* graph. But when adding an edge, we have to add it in both directions since it is bidirectional.