Topological sorting

Author: ivanmmarkovic

Ch07. Graphs and Graph Algorithms/topological-sorting/__pycache__/graph.cpython-39.pyc

@@ -11,18 +11,18 @@ def __init__(self):
         self.no_incoming_edges: dict = {} # to avoid looking through whole list
         self.explored: list = []
 
-    def addVertex(self, label: str):
+    def add_vertex(self, label: str):
         self.vertices.append(label)
         self.adjacencyList[label]: list = []
         self.colors[label] = "white"
         self.distance[label] = 0
         self.previous[label] = None
         self.no_incoming_edges[label] = label
 
-    def addEdge(self, label1: str, label2: str):
+    def add_edge(self, label1: str, label2: str):
         self.adjacencyList[label1].append(label2)
         if label2 in self.no_incoming_edges:
-            del self.no_incoming_edges[label2] # remove vertex, it has incoming edge
+            del self.no_incoming_edges[label2]  # remove vertex, it has incoming edge
 
     def topsort(self):
         # perform depth first search on vertices with no incoming edges
@@ -45,9 +45,9 @@ def dfs(self, start: str):
         self.colors[start] = "black"
         self.explored.append(start)
 
-    def showPath(self, label: str)->str:
+    def show_path(self, label: str) -> str:
         if self.previous[label] is None:
             return label
         else:
-            return self.showPath(self.previous[label]) + " -> " + label
+            return self.show_path(self.previous[label]) + " -> " + label
 

Ch07. Graphs and Graph Algorithms/topological-sorting/graph.py

@@ -4,14 +4,14 @@
 
 vertices = ["a", "b", "c", "d", "e", "f"]
 for vertex in vertices:
-    graph.addVertex(vertex)
+    graph.add_vertex(vertex)
 
 
-graph.addEdge("a", "c")
-graph.addEdge("c", "d")
-graph.addEdge("c", "f")
-graph.addEdge("b", "c")
-graph.addEdge("b", "e")
+graph.add_edge("a", "c")
+graph.add_edge("c", "d")
+graph.add_edge("c", "f")
+graph.add_edge("b", "c")
+graph.add_edge("b", "e")
 
 graph.topsort()
 

Ch07. Graphs and Graph Algorithms/topological-sorting/main.py

@@ -0,0 +1,53 @@
+class Graph:
+    def __init__(self):
+        self.vertices: list = []
+        self.adjacencyList: dict = {}
+        self.colors: dict = {}
+        self.previous: dict = {}
+        self.distance: dict = {}
+        self.time: int = 0
+        self.entry: dict = {}
+        self.exit: dict = {}
+        self.no_incoming_edges: dict = {} # to avoid looking through whole list
+        self.explored: list = []
+
+    def add_vertex(self, label: str):
+        self.vertices.append(label)
+        self.adjacencyList[label]: list = []
+        self.colors[label] = "white"
+        self.distance[label] = 0
+        self.previous[label] = None
+        self.no_incoming_edges[label] = label
+
+    def add_edge(self, label1: str, label2: str):
+        self.adjacencyList[label1].append(label2)
+        if label2 in self.no_incoming_edges:
+            del self.no_incoming_edges[label2]  # remove vertex, it has incoming edge
+
+    def topsort(self):
+        # perform depth first search on vertices with no incoming edges
+        for label in self.no_incoming_edges:
+            self.dfs(label)
+        self.explored.reverse()
+        print(self.explored)
+
+    def dfs(self, start: str):
+        self.time += 1
+        self.entry[start] = self.time
+        self.colors[start] = "gray"
+        for neighbour in self.adjacencyList[start]:
+            if self.colors[neighbour] == "white":
+                self.previous[neighbour] = start
+                self.distance[neighbour] = self.distance[neighbour] + 1
+                self.dfs(neighbour)
+        self.time += 1
+        self.exit[start] = self.time
+        self.colors[start] = "black"
+        self.explored.append(start)
+
+    def show_path(self, label: str) -> str:
+        if self.previous[label] is None:
+            return label
+        else:
+            return self.show_path(self.previous[label]) + " -> " + label
+

graphs/topological-sorting/graph.py

@@ -0,0 +1,17 @@
+from graph import Graph
+
+graph = Graph()
+
+vertices = ["a", "b", "c", "d", "e", "f"]
+for vertex in vertices:
+    graph.add_vertex(vertex)
+
+
+graph.add_edge("a", "c")
+graph.add_edge("c", "d")
+graph.add_edge("c", "f")
+graph.add_edge("b", "c")
+graph.add_edge("b", "e")
+
+graph.topsort()
+