G.addVertex('d')
G.addVertex('e')
G.addEdge('a', 'b', 1)
G.addEdge('a', 'c', 1)
G.addEdge('b', 'd', 1)
G.addEdge('b', 'e', 1)
G.addEdge('c', 'd', 1)
G.addEdge('c', 'e', 1)
G.addEdge('d', 'e', 1)
G.addEdge('e', 'a', 1)
print has_cycle(G,G.getVertex('a'))
#existence of a cycle in a directed graph
DG = DirectedGraph()
DG.addVertex('a')
DG.addVertex('b')
DG.addVertex('c')
DG.addVertex('d')
DG.addVertex('e')
DG.addEdge('a', 'b', 1)
DG.addEdge('b', 'c', 1)
DG.addEdge('c', 'd', 1)
DG.addEdge('e', 'a', 1)
DG.addEdge('e', 'c', 1)
print has_cycle(DG,DG.getVertex('a'))
# topologicalSortedNodes = topologicalSort(G,G.getVertex('a'))
DG = DirectedGraph()
DG.addVertex('a')
DG.addVertex('b')
DG.addVertex('c')
DG.addVertex('d')
DG.addVertex('e')
DG.addVertex('f')
DG.addVertex('g')
DG.addVertex('h')
DG.addVertex('i')
DG.addEdge('a', 'd', 1)
DG.addEdge('b', 'd', 1)
DG.addEdge('c', 'd', 1)
DG.addEdge('d', 'g', 1)
DG.addEdge('d', 'e', 1)
DG.addEdge('g', 'h', 1)
DG.addEdge('f', 'e', 1)
DG.addEdge('e', 'i', 1)
DG.addEdge('i', 'h', 1)
topologicalSort(DG)
DG1 = DirectedGraph()
DG1.addVertex('a')
DG1.addVertex('b')
DG1.addVertex('c')
topologicalSort(G)
# topologicalSortedNodes = topologicalSort(G,G.getVertex('a'))
DG = DirectedGraph()
DG.addVertex('a')
DG.addVertex('b')
DG.addVertex('c')
DG.addVertex('d')
DG.addVertex('e')
DG.addVertex('f')
DG.addVertex('g')
DG.addVertex('h')
DG.addVertex('i')
DG.addEdge('a', 'd', 1)
DG.addEdge('b', 'd', 1)
DG.addEdge('c', 'd', 1)
DG.addEdge('d', 'g', 1)
DG.addEdge('d', 'e', 1)
DG.addEdge('g', 'h', 1)
DG.addEdge('f', 'e', 1)
DG.addEdge('e', 'i', 1)
DG.addEdge('i', 'h', 1)
topologicalSort(DG)
DG1 = DirectedGraph()
DG1.addVertex('a')
DG1.addVertex('b')
DG1.addVertex('c')