Tighten up psf/black and flake8 (#2024)

* Tighten up psf/black and flake8

* Fix some tests

* Fix some E741

* Fix some E741

* updating DIRECTORY.md

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

graphs/kahns_algorithm_topo.py

@@ -1,11 +1,14 @@
-# Kahn's Algorithm is used to find Topological ordering of Directed Acyclic Graph using BFS
-def topologicalSort(l):
-    indegree = [0] * len(l)
+def topologicalSort(graph):
+    """
+    Kahn's Algorithm is used to find Topological ordering of Directed Acyclic Graph
+    using BFS
+    """
+    indegree = [0] * len(graph)
     queue = []
     topo = []
     cnt = 0
 
-    for key, values in l.items():
+    for key, values in graph.items():
         for i in values:
             indegree[i] += 1
 
@@ -17,17 +20,17 @@ def topologicalSort(l):
         vertex = queue.pop(0)
         cnt += 1
         topo.append(vertex)
-        for x in l[vertex]:
+        for x in graph[vertex]:
             indegree[x] -= 1
             if indegree[x] == 0:
                 queue.append(x)
 
-    if cnt != len(l):
+    if cnt != len(graph):
         print("Cycle exists")
     else:
         print(topo)
 
 
 # Adjacency List of Graph
-l = {0: [1, 2], 1: [3], 2: [3], 3: [4, 5], 4: [], 5: []}
-topologicalSort(l)
+graph = {0: [1, 2], 1: [3], 2: [3], 3: [4, 5], 4: [], 5: []}
+topologicalSort(graph)