Update graph.py

Author: ivanmmarkovic

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

@@ -1,39 +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 addVertex(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):
         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):
-        for vertex in self.vertices:
-            if self.colors[vertex] == "white":
-                self.dfs(vertex)
+        # 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, label: str):
-        self.colors[label] = "gray"
-        for neighbour in self.adjacencyList[label]:
+
+    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.colors[neighbour] = "gray"
+                self.previous[neighbour] = start
+                self.distance[neighbour] = self.distance[neighbour] + 1
                 self.dfs(neighbour)
-        self.explored.append(label)
-        self.colors[label] = "black"
-
-
-
-
-
-            
-
+        self.time += 1
+        self.exit[start] = self.time
+        self.colors[start] = "black"
+        self.explored.append(start)
+
+    def showPath(self, label: str)->str:
+        if self.previous[label] is None:
+            return label
+        else:
+            return self.showPath(self.previous[label]) + " -> " + label