Added topological sort for DAG.

Author: shivansh-sopho

Mathematical_Algorithms/src/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 the 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()