Added functions to check cycle in directed and undirected graph

Author: OmkarPathak

pygorithm/data_structures/graph.py

@@ -1,7 +1,7 @@
 # Author: OMKAR PATHAK
 # Created On: 12th August 2017
 
-class AdjacencyList(object):
+class Graph(object):
     def __init__(self):
         self.graph = {}
         self.count = 0
@@ -24,9 +24,9 @@ def add_edge(self, from_vertex, to_vertex):
     def get_code(self):
         ''' returns the code for the current class '''
         import inspect
-        return inspect.getsource(AdjacencyList)
+        return inspect.getsource(Graph)
 
-class TopologicalSort(AdjacencyList):
+class TopologicalSort(Graph):
     def topological_sort(self):
         visited = [False] * self.count           # Marking all vertices as not visited
         stack = []                               # Stack for storing the vertex
@@ -58,3 +58,103 @@ def get_code(self):
         ''' returns the code for the current class '''
         import inspect
         return inspect.getsource(TopologicalSort)
+
+class CheckCycleDirected(object):
+    def __init__(self):
+        self.graph = {}
+        self.count = 0
+
+    def print_graph(self):
+        ''' for printing the contents of the graph '''
+        for i  in self.graph:
+            print(i,'->',' -> '.join([str(j) for j in self.graph[i]]))
+
+    def add_edge(self, from_vertex, to_vertex):
+        ''' function to add an edge in the graph '''
+        # check if vertex is already present
+        if from_vertex in self.graph.keys():
+            self.graph[from_vertex].append(to_vertex)
+            self.count += 1
+        else:
+            self.graph[from_vertex] = [to_vertex]
+            self.count += 1
+
+    def check_cycle(self):
+        ''' This function will return True if graph is cyclic else return False '''
+        visited = [False] * len(self.graph)
+        stack = [False] * len(self.graph)
+        for vertex in range(len(self.graph)):
+            if visited[vertex] == False:
+                if self.check_cycle_rec(visited, stack, vertex) == True:
+                    return True
+        return False
+
+    def check_cycle_rec(self, visited, stack, vertex):
+        ''' Recursive function for finding the cycle '''
+        # Mark the current node in visited and also add it to the stack
+        visited[vertex] = True
+        stack[vertex] = True
+
+        # mark all adjacent nodes of the current node
+        for adjacentNode in self.graph[vertex]:
+            if visited[adjacentNode] == False:
+                if self.check_cycle_rec(visited, stack, adjacentNode) == True:
+                    return True
+            elif stack[adjacentNode] == True:
+                return True
+
+        # The node needs to be poped from
+        # recursion stack before function ends
+        stack[vertex] = False
+        return False
+
+    def get_code(self):
+        ''' returns the code for the current class '''
+        import inspect
+        return inspect.getsource(CheckCycleDirected)
+
+class CheckCycleUndirected(object):
+    def __init__(self):
+        self.graph = {}
+        self.count = 0
+
+    def print_graph(self):
+        ''' for printing the contents of the graph '''
+        for i  in self.graph:
+            print(i,'->',' -> '.join([str(j) for j in self.graph[i]]))
+
+    def add_edge(self, fromVertex, toVertex):
+        ''' for adding the edge beween two vertices '''
+        # check if vertex is already present,
+        if fromVertex in self.graph.keys() and toVertex in self.graph.keys():
+            self.graph[fromVertex].append(toVertex)
+            self.graph[toVertex].append(fromVertex)
+        else:
+            # else make a new vertex
+            self.graph[fromVertex] = [toVertex]
+            self.graph[toVertex] = [fromVertex]
+
+    def check_cycle(self):
+        ''' This function will return True if graph is cyclic else return False '''
+        visited = [False] * len(self.graph)            # Marking all vertices as not visited
+        for vertex in range(len(self.graph)):
+            # Call the recursive function only if not visited
+            if visited[vertex] == False:
+                if self.check_cycle_rec(visited, -1, vertex) == True:
+                    return True
+        return False
+
+    def check_cycle_rec(self, visited, parent, vertex):
+        ''' Recursive function for finding the cycle '''
+        # Mark the current node in visited
+        visited[vertex] = True
+
+        # mark all adjacent nodes of the current node
+        for adjacentNode in self.graph[vertex]:
+            if visited[adjacentNode] == False:
+                if self.check_cycle_rec(visited, vertex, adjacentNode) == True:
+                    return True
+            elif parent != adjacentNode:
+                return True
+
+        return False