fix: graph6 and digraph6 labelings

Before, we were iterating through list of vertices incorrectly

src/graph_utils.py

@@ -174,16 +174,13 @@ def print_labelg(self):
             with open(labels_file_output, "r") as file:
 
                 # Clear previous contents of the labelg output file
-                labelg_output_file = os.path.join(
-                    output_dir, "labelg_output.txt"
-                )
+                labelg_output_file = os.path.join(output_dir, "labelg_output.txt")
                 with open(labelg_output_file, "w") as labelg_file:
                     labelg_file.write("")
 
                 for line in file:
                     line = line.strip()
-                    if self.graph_type == GraphType.DIRECTED:
-                        line = "&" + line
+
                     result = subprocess.run(
                         [label_g],
                         input=line + "\n",

src/labeling.py

@@ -5,18 +5,34 @@
 def graph6(graph: nx.Graph) -> str:
     """
     Convert a subgraph into graph6 format.
+
+    Parameters:
+        graph (nx.Graph): A NetworkX graph.
+
+    Returns:
+        str: The graph6 encoded string.
     """
     # Step 1: Compute N(n), the graph size character
-    graph_size = graph.order()
-    N = chr(graph_size + 63)
+    graph_size = graph.order()  # number of nodes in the graph
+    vertices = list(graph.nodes())
+
+    if graph_size == 0:
+        return ""  # empty graph
+    elif graph_size == 1:
+        return ""  # single-node graph
+
+    N = chr(graph_size + 63)  # add 63 to graph_size
 
     # Step 2: Compute R(x). Create bit vector from the upper triangle of the
     # adjacency matrix
     # For undirected: read upper triangle of the matrix, column by column
     bit_vector = []
-    for c in range(graph_size):
-        for r in range(c):
-            bit_vector.append(1 if graph.has_edge(r, c) else 0)
+    for r in vertices:
+        for c in vertices:
+            if (graph.has_edge(r, c)):
+                bit_vector.append(1)
+            else:
+                bit_vector.append(0)
 
     # Step 3: Pad bit vector with zeros to make its length a multiple of 6
     while len(bit_vector) % 6 != 0:
@@ -34,18 +50,34 @@ def graph6(graph: nx.Graph) -> str:
 def digraph6(graph: nx.DiGraph) -> str:
     """
     Convert a directed subgraph into digraph6 format.
+
+    Parameters:
+        graph (nx.Graph): A NetworkX graph.
+
+    Returns:
+        str: The digraph6 encoded string.
     """
     # Step 1: Compute N(n), the graph size character
     graph_size = graph.order()
+    vertices = list(graph.nodes)
+
+    if graph_size == 0:
+        return ""  # empty graph
+    elif graph_size == 1:
+        return ""  # single-node graph
+
     N = chr(graph_size + 63)
 
     # Step 2: Compute R(x). Create bit vector from the upper triangle of the
     # adjacency matrix
     # For directed: read the matrix row by row
     bit_vector = []
-    for r in range(graph_size):
-        for c in range(graph_size):
-            bit_vector.append(1 if graph.has_edge(r, c) else 0)
+    for r in vertices:
+        for c in vertices:
+            if (graph.has_edge(r, c)):
+                bit_vector.append(1)
+            else:
+                bit_vector.append(0)
 
     # Step 3: Pad bit vector with zeros to make its length a multiple of 6
     while len(bit_vector) % 6 != 0:
@@ -57,8 +89,9 @@ def digraph6(graph: nx.DiGraph) -> str:
         group = bit_vector[i : i + 6]
         group_value = sum((bit << (5 - idx)) for idx, bit in enumerate(group))
         R += chr(group_value + 63)
+        print(R)
 
-    return N + R
+    return chr(38) + N + R
 
 
 def get_graph_label(nx_graph: nx.Graph, graph_type: GraphType) -> str: