Graph list patch (#4113)

* new implementation for adjacency list graph

* add example code for undirected graph

* reduce length to 88 columns max to fix build errors7

* fix pre commit issues

* replace print_list method with __str__

* return object in add_edge method to enable fluent syntax

* improve class docstring and include doctests

* add end of file line

* fix pre-commit issues

* remove __str__ method

* trigger build

* Update graph_list.py

* Update graph_list.py

Co-authored-by: gnc <chidieberen1999@gmail.com>
Co-authored-by: Christian Clauss <cclauss@me.com>

graphs/graph_list.py

@@ -1,44 +1,143 @@
-#!/usr/bin/python
+#!/usr/bin/env python3
 
-# Author: OMKAR PATHAK
+# Author: OMKAR PATHAK, Nwachukwu Chidiebere
 
-# We can use Python's dictionary for constructing the graph.
+# Use a Python dictionary to construct the graph.
+
+from pprint import pformat
 
 
-class AdjacencyList:
+class GraphAdjacencyList:
-    def __init__(self):
+    """
-        self.adj_list = {}
+    Adjacency List type Graph Data Structure that accounts for directed and undirected
+    Graphs.  Initialize graph object indicating whether it's directed or undirected.
 
-    def add_edge(self, from_vertex: int, to_vertex: int) -> None:
+    Directed graph example:
-        # check if vertex is already present
+    >>> d_graph = GraphAdjacencyList()
-        if from_vertex in self.adj_list:
+    >>> d_graph
-            self.adj_list[from_vertex].append(to_vertex)
+    {}
-        else:
+    >>> d_graph.add_edge(0, 1)
-            self.adj_list[from_vertex] = [to_vertex]
+    {0: [1], 1: []}
+    >>> d_graph.add_edge(1, 2).add_edge(1, 4).add_edge(1, 5)
+    {0: [1], 1: [2, 4, 5], 2: [], 4: [], 5: []}
+    >>> d_graph.add_edge(2, 0).add_edge(2, 6).add_edge(2, 7)
+    {0: [1], 1: [2, 4, 5], 2: [0, 6, 7], 4: [], 5: [], 6: [], 7: []}
+    >>> print(d_graph)
+    {0: [1], 1: [2, 4, 5], 2: [0, 6, 7], 4: [], 5: [], 6: [], 7: []}
+    >>> print(repr(d_graph))
+    {0: [1], 1: [2, 4, 5], 2: [0, 6, 7], 4: [], 5: [], 6: [], 7: []}
 
-    def print_list(self) -> None:
+    Undirected graph example:
-        for i in self.adj_list:
+    >>> u_graph = GraphAdjacencyList(directed=False)
-            print((i, "->", " -> ".join([str(j) for j in self.adj_list[i]])))
+    >>> u_graph.add_edge(0, 1)
+    {0: [1], 1: [0]}
+    >>> u_graph.add_edge(1, 2).add_edge(1, 4).add_edge(1, 5)
+    {0: [1], 1: [0, 2, 4, 5], 2: [1], 4: [1], 5: [1]}
+    >>> u_graph.add_edge(2, 0).add_edge(2, 6).add_edge(2, 7)
+    {0: [1, 2], 1: [0, 2, 4, 5], 2: [1, 0, 6, 7], 4: [1], 5: [1], 6: [2], 7: [2]}
+    >>> u_graph.add_edge(4, 5)
+    {0: [1, 2],
+     1: [0, 2, 4, 5],
+     2: [1, 0, 6, 7],
+     4: [1, 5],
+     5: [1, 4],
+     6: [2],
+     7: [2]}
+    >>> print(u_graph)
+    {0: [1, 2],
+     1: [0, 2, 4, 5],
+     2: [1, 0, 6, 7],
+     4: [1, 5],
+     5: [1, 4],
+     6: [2],
+     7: [2]}
+    >>> print(repr(u_graph))
+    {0: [1, 2],
+     1: [0, 2, 4, 5],
+     2: [1, 0, 6, 7],
+     4: [1, 5],
+     5: [1, 4],
+     6: [2],
+     7: [2]}
+    """
+
+    def __init__(self, directed: bool = True):
+        """
+        Parameters:
+        directed: (bool) Indicates if graph is directed or undirected. Default is True.
+        """
+
+        self.adj_list = {}  # dictionary of lists
+        self.directed = directed
+
+    def add_edge(self, source_vertex: int, destination_vertex: int) -> object:
+        """
+        Connects vertices together. Creates and Edge from source vertex to destination
+        vertex.
+        Vertices will be created if not found in graph
+        """
+
+        if not self.directed:  # For undirected graphs
+            # 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]
+        else:  # For directed graphs
+            # 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] = []
+
+        return self
+
+    def __repr__(self) -> str:
+        return pformat(self.adj_list)
 
 
 if __name__ == "__main__":
-    al = AdjacencyList()
+    import doctest
-    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, 2)
-    al.add_edge(2, 3)
-    al.add_edge(3, 4)
 
-    al.print_list()
+    doctest.testmod()
-
-    # OUTPUT:
-    # 0 -> 1 -> 4
-    # 1 -> 0 -> 4 -> 3 -> 2
-    # 2 -> 3
-    # 3 -> 4
-    # 4 -> 1 -> 3