Merge pull request #116 from Sarbamoy/patch-1

Topological_sort.py

Sorting Algorithms/Python/topological_sort.py

@@ -0,0 +1,53 @@
+#Python program to print topological sorting of a DAG
+from collections import defaultdict
+
+#Class to represent a graph
+class Graph:
+    def __init__(self,vertices):
+        self.graph = defaultdict(list) #dictionary containing adjacency List
+        self.V = vertices #No. of vertices
+
+    # function to add an edge to graph
+    def addEdge(self,u,v):
+        self.graph[u].append(v)
+
+    # A recursive function used by topologicalSort
+    def topologicalSortUtil(self,v,visited,stack):
+
+        # Mark the current node as visited.
+        visited[v] = True
+
+        # Recur for all the vertices adjacent to this vertex
+        for i in self.graph[v]:
+            if visited[i] == False:
+                self.topologicalSortUtil(i,visited,stack)
+
+        # Push current vertex to stack which stores result
+        stack.insert(0,v)
+
+    # The function to do Topological Sort. It uses recursive 
+    # topologicalSortUtil()
+    def topologicalSort(self):
+        # Mark all the vertices as not visited
+        visited = [False]*self.V
+        stack =[]
+
+        # Call the recursive helper function to store Topological
+        # Sort starting from all vertices one by one
+        for i in range(self.V):
+            if visited[i] == False:
+                self.topologicalSortUtil(i,visited,stack)
+
+        # Print contents of stack
+        print stack
+
+g= Graph(6)
+g.addEdge(5, 2);
+g.addEdge(5, 0);
+g.addEdge(4, 0);
+g.addEdge(4, 1);
+g.addEdge(2, 3);
+g.addEdge(3, 1);
+
+print "Following is a Topological Sort of the given graph"
+g.topologicalSort()