Topological sort using Adjacency Lists

graphs/topological_sort.py

@@ -0,0 +1,52 @@
+#Topological sort is for "Directed and Acyclic Graphs"
+#Time complexity O(V+E)
+#Topological ordering is an ordering from node u -> v such that,
+#node u is always placed befor node v in the ordering
+# you can modify this code for any implementation
+g = {  0:[1],
+       1:[2],
+       2:[3],
+       3:[4],
+       4:[5],
+       5:[6],
+       6:[7],
+       7:[8],
+       8:[9],
+       9:[10],
+       10:[11],
+       11:[]}
+N = len(g)
+V = [False for i in range(N)]
+def dfs(at,visitedNodes):
+    V[at] = True
+
+    # print("Neighbours of {} are {}".format(at,g[at]))
+
+    for next in g[at]: 
+        if V[next] == False:
+            # print("Visited:",V)
+            dfs(next,visitedNodes)
+
+    # print('Visited nodes list:',visitedNodes)
+
+    visitedNodes.append(at)
+
+def topsort():
+    ordering = [0 for i in range(N)]
+    i = N-1  #Index for ordering array
+
+    for at in range(N):  #For each node in the graph run DFS on it if unvisited
+
+        # print("Calling DFS for:",at)
+
+        if V[at] == False:
+            visitedNodes = []
+            dfs(at,visitedNodes)
+            for nodeId in visitedNodes:
+                ordering[i] = nodeId
+                i -= 1
+
+    # print(ordering)
+
+    return ordering
+print(topsort())