Graph list patch

graphs/graph_list.py

@@ -1,44 +1,153 @@
 #!/usr/bin/python
 
-# Author: OMKAR PATHAK
+# Author: OMKAR PATHAK, Nwachukwu Chidiebere
 
 # We can use Python's dictionary for constructing the graph.
 
+from pprint import pformat, pprint
 
-class AdjacencyList:
-    def __init__(self):
-        self.adj_list = {}
 
-    def add_edge(self, from_vertex: int, to_vertex: int) -> None:
-        # check if vertex is already present
-        if from_vertex in self.adj_list:
-            self.adj_list[from_vertex].append(to_vertex)
+class GraphAdjacencyList:
+    """
+    Adjacency List type Graph Data Structure that accounts for directed and undirected
+    Graphs.
+    """
+    def __init__(self, directed=True):
+        """
+        Initialize graph object indicating whether it's directed or undirected. Default
+        is directed.
+
+        Parameters
+        ----------
+            directed (bool): Indicates if graph is directed or undirected. Default is
+            directed (True).
+        """
+        self.adj_list = {}  # dictionary of lists
+        self.directed = directed
+
+    def add_edge(self, source_vertex: int, destination_vertex: int) -> None:
+        """
+        Connects vertices together. Creates and Edge from source vertex to destination
+        vertex.
+        Vertices will be created if not found in graph
+        """
+
+        # For undirected graphs
+        if not self.directed:
+            # if both source vertex and destination vertex are both present in the
+            # adjacency list, add destination vertex to source vertex list of adjacent
+            # vertices and add source vertex to destination vertex list of adjacent
+            # vertices.
+            if source_vertex in self.adj_list and destination_vertex in self.adj_list:
+                self.adj_list[source_vertex].append(destination_vertex)
+                self.adj_list[destination_vertex].append(source_vertex)
+            # if only source vertex is present in adjacency list, add destination vertex
+            # to source vertex list of adjacent vertices, then create a new vertex with
+            # destination vertex as key and assign a list containing the source vertex
+            # as it's first adjacent vertex.
+            elif source_vertex in self.adj_list:
+                self.adj_list[source_vertex].append(destination_vertex)
+                self.adj_list[destination_vertex] = [source_vertex]
+            # if only destination vertex is present in adjacency list, add source vertex
+            # to destination vertex list of adjacent vertices, then create a new vertex
+            # with source vertex as key and assign a list containing the source vertex
+            # as it's first adjacent vertex.
+            elif destination_vertex in self.adj_list:
+                self.adj_list[destination_vertex].append(source_vertex)
+                self.adj_list[source_vertex] = [destination_vertex]
+            # if both source vertex and destination vertex are not present in adjacency
+            # list, create a new vertex with source vertex as key and assign a list
+            # containing the destination vertex as it's first adjacent vertex also
+            # create a new vertex with destination vertex as key and assign a list
+            # containing the source vertex as it's first adjacent vertex.
+            else:
+                self.adj_list[source_vertex] = [destination_vertex]
+                self.adj_list[destination_vertex] = [source_vertex]
+
+        # For directed Graphs
         else:
-            self.adj_list[from_vertex] = [to_vertex]
+            # if both source vertex and destination vertex are present in adjacency
+            # list, add destination vertex to source vertex list of adjacent vertices.
+            if source_vertex in self.adj_list and destination_vertex in self.adj_list:
+                self.adj_list[source_vertex].append(destination_vertex)
+            # if only source vertex is present in adjacency list, add destination vertex
+            # to source vertex list of adjacent vertices and create a new vertex with
+            # destination vertex as key, which has no adjacent vertex.
+            elif source_vertex in self.adj_list:
+                self.adj_list[source_vertex].append(destination_vertex)
+                self.adj_list[destination_vertex] = []
+            # if only destination vertex is present in adjacency list, create a new
+            # vertex with source vertex as key and assign a list containing destination
+            # vertex as first adjacent vertex.
+            elif destination_vertex in self.adj_list:
+                self.adj_list[source_vertex] = [destination_vertex]
+            # if both source vertex and destination vertex are not present in adjacency
+            # list, create a new vertex with source vertex as key and a list containing
+            # destination vertex as it's first adjacent vertex. Then create a new vertex
+            # with destination vertex as key, which has no adjacent vertex.
+            else:
+                self.adj_list[source_vertex] = [destination_vertex]
+                self.adj_list[destination_vertex] = []
 
     def print_list(self) -> None:
-        for i in self.adj_list:
-            print((i, "->", " -> ".join([str(j) for j in self.adj_list[i]])))
+        """
+        Displays adjacency list using python's pretty print function
+        """
+        pprint(self.adj_list)
+
+    def __repr__(self) -> str:
+        return pformat(self.adj_list)
 
 
 if __name__ == "__main__":
-    al = AdjacencyList()
+    # directed graph
+    al = GraphAdjacencyList()
     al.add_edge(0, 1)
-    al.add_edge(0, 4)
-    al.add_edge(4, 1)
-    al.add_edge(4, 3)
-    al.add_edge(1, 0)
-    al.add_edge(1, 4)
     al.add_edge(1, 3)
+    al.add_edge(1, 4)
     al.add_edge(1, 2)
-    al.add_edge(2, 3)
-    al.add_edge(3, 4)
+    al.add_edge(3, 7)
+    al.add_edge(3, 9)
+    al.add_edge(4, 5)
+    al.add_edge(4, 6)
+    al.add_edge(2, 8)
 
     al.print_list()
 
     # OUTPUT:
-    # 0 -> 1 -> 4
-    # 1 -> 0 -> 4 -> 3 -> 2
-    # 2 -> 3
-    # 3 -> 4
-    # 4 -> 1 -> 3
+    # {0: [1],
+    #  1: [3, 4, 2],
+    #  2: [8],
+    #  3: [7, 9],
+    #  4: [5, 6],
+    #  5: [],
+    #  6: [],
+    #  7: [],
+    #  8: [],
+    #  9: []}
+
+    # Undirected graph
+    al2 = GraphAdjacencyList(False)
+    al2.add_edge(0, 1)
+    al2.add_edge(1, 3)
+    al2.add_edge(1, 4)
+    al2.add_edge(1, 2)
+    al2.add_edge(3, 7)
+    al2.add_edge(3, 9)
+    al2.add_edge(4, 5)
+    al2.add_edge(4, 6)
+    al2.add_edge(2, 8)
+
+    al2.print_list()
+
+    # OUTPUT:
+    # {0: [1],
+    #  1: [0, 3, 4, 2],
+    #  2: [1, 8],
+    #  3: [1, 7, 9],
+    #  4: [1, 5, 6],
+    #  5: [4],
+    #  6: [4],
+    #  7: [3],
+    #  8: [2],
+    #  9: [3]}