def worst_case_graph(self,k):
        # see figure 1 in Johnson's paper
        # this graph has excactly 3k simple cycles
        G=nx.DiGraph()
        for n in range(2,k+2):
            G.add_edge(1,n)
            G.add_edge(n,k+2)
        G.add_edge(2*k+1,1)
        for n in range(k+2,2*k+2):
            G.add_edge(n,2*k+2)
            G.add_edge(n,n+1)
        G.add_edge(2*k+3,k+2)
        for n in range(2*k+3,3*k+3):
            G.add_edge(2*k+2,n)
            G.add_edge(n,3*k+3)
        G.add_edge(3*k+3,2*k+2)
        return G
dataset/ETHPy150Open gkno/gkno_launcher/src/networkx/algorithms/tests/test_cycles.py/TestCycles.worst_case_graph/original