Added a function to delete a Node and its associated Edges (#24)

* Added a function to delete a Node and its associated Edges

* Requested changes

graph.go

@@ -149,6 +149,28 @@ func (g *Graph) Node(id string) Node {
 	return n
 }
 
+// DeleteNode deletes a node and all the edges associated to the node
+// Returns false if the node wasn't found, true otherwise
+func (g *Graph) DeleteNode(id string) bool {
+	if _, ok := g.findNode(id); ok {
+		// Remove Node
+		delete(g.nodes, id)
+		// Remove all the edges from the Node
+		delete(g.edgesFrom, id)
+		// Remove all the edges to the Node
+		for parent, edgeList := range g.edgesFrom {
+			for i, edge := range edgeList {
+				if edge.to.id == id {
+					g.edgesFrom[parent] = append(g.edgesFrom[parent][:i], g.edgesFrom[parent][i+1:]...)
+					break
+				}
+			}
+		}
+		return true
+	}
+	return false
+}
+
 // Edge creates a new edge between two nodes.
 // Nodes can be have multiple edges to the same other node (or itself).
 // If one or more labels are given then the "label" attribute is set to the edge.

graph_test.go

@@ -34,6 +34,34 @@ func TestEmptyWithHTMLLabel(t *testing.T) {
 	}
 }
 
+func TestDeleteNode(t *testing.T) {
+	di := NewGraph(Directed)
+	n1 := di.Node("A")
+	n2 := di.Node("B")
+	n3 := di.Node("C")
+	di.Edge(n1, n2) // Will be deleted
+	di.Edge(n2, n3) // Will also be deleted
+	di.Edge(n1, n3) // Must not be deleted
+	wasDeleted := di.DeleteNode("B")
+	if got, want := flatten(di.String()), `digraph  {n1[label="A"];n3[label="C"];n1->n3;}`; wasDeleted && got != want {
+		t.Errorf("got [%v] want [%v]", got, want)
+	}
+}
+
+func TestDeleteNodeWhenNodeDoesNotExist(t *testing.T) {
+	di := NewGraph(Directed)
+	n1 := di.Node("A")
+	n2 := di.Node("B")
+	n3 := di.Node("C")
+	di.Edge(n1, n2)
+	di.Edge(n2, n3)
+	wasDeleted := di.DeleteNode("D")
+
+	if got, want := flatten(di.String()), `digraph  {n1[label="A"];n2[label="B"];n3[label="C"];n1->n2;n2->n3;}`; !wasDeleted && got != want {
+		t.Errorf("got [%v] want [%v]", got, want)
+	}
+}
+
 func TestEmptyWithLiteralValueLabel(t *testing.T) {
 	di := NewGraph(Directed)
 	di.ID("test")