Add topological-sorting.py

Author: ivanmmarkovic

Ch07. Graphs and Graph Algorithms/Topological Sorting/topological-sorting.py

@@ -0,0 +1,89 @@
+from Stack import Stack
+from collections import OrderedDict
+
+class Graph:
+    def __init__(self):
+        self.vertices = []
+        self.adjacencyList = {}
+        self.distance = {}
+        self.previous = {}
+        self.visited = []
+
+    def add_vertex(self, v):
+        self.vertices.append(v)
+        self.adjacencyList[v] = []
+        self.distance[v] = 0
+        self.previous[v] = None
+
+    def add_edge(self,v1, v2):
+        self.adjacencyList[v1].append(v2)
+        #self.adjacencyList[v2].append(v1) DIRECTED ACYCLIC GRAPHS ONLY
+
+    def to_string(self):
+        result = ""
+        for vertex in self.vertices:
+            result += (vertex + " -> ")
+            for neighbour in self.adjacencyList[vertex]:
+                result += neighbour + " "
+            result += "\n"
+        return result
+
+    def breadth_first_search(self):
+        for vertex in self.vertices:
+            self.search_helper(vertex)
+
+        sorted_x = sorted(self.distance.items(), key=lambda kv: kv[1])
+        sorted_dict = OrderedDict(sorted_x)
+        print(sorted_dict)
+
+    def search_helper(self, vertex):
+        self.visited.append(vertex)
+        stack = Stack()
+        stack.push(vertex)
+        self.visited.append(vertex)
+        while not stack.isEmpty():
+            peeked_vertex = stack.peek()
+            new_vertex = self.find_unvisited_neighbour(peeked_vertex)
+            if new_vertex != None:
+                self.previous[new_vertex] = peeked_vertex
+                self.distance[new_vertex] = self.distance[peeked_vertex] + 1
+                self.visited.append(new_vertex)
+                stack.push(new_vertex)
+            else:
+                stack.pop()
+
+    def find_unvisited_neighbour(self, vertex):
+        found = False
+        count = 0
+        while count < len(self.adjacencyList[vertex]) and not found:
+            if self.adjacencyList[vertex][count] not in self.visited:
+                found =True
+            else:
+                count +=1
+        if found:
+            return self.adjacencyList[vertex][count]
+        else:
+            return None
+
+graph = Graph()
+
+
+vertices = ['A', 'B', 'C', 'D', 'E']
+# add vertices
+for i in range(len(vertices)):
+    graph.add_vertex(vertices[i])
+
+graph.add_edge('A', 'B')
+graph.add_edge('C', 'B')
+graph.add_edge('B', 'D')
+graph.add_edge('D', 'E')
+
+print(graph.to_string())
+print("##########################")
+graph.breadth_first_search()
+print(graph.distance)
+print(graph.previous)
+print(graph.distance)
+
+
+