      "* If we try to add a node that already exists, do we just do nothing?\n",
      "    * Yes\n",
      "* If we try to delete a node that doesn't exist, do we just do nothing?\n",
      "    * Yes\n",
      "* Can we assume the inputs are valid?\n",
      "    * Yes\n",
      "* Can we assume this fits memory?\n",
      "    * Yes"
     ]
 
</s>
    "* Can we assume this is a connected graph?\n",
    "    * Yes\n",
      "* If we try to add a node that already exists, do we just do nothing?\n",
      "    * Yes\n",
      "* If we try to delete a node that doesn't exist, do we just do nothing?\n",
      "    * Yes\n",
    "* Can we assume this is a connected graph?\n",
    "    * Yes\n",
      "* Can we assume the inputs are valid?\n",
      "    * Yes\n",
      "* Can we assume this fits memory?\n",
      "    * Yes"
     ]
keep keep keep add keep keep keep keep keep
 Update graphs challenges to add connected constraint (#151)
graphs_trees/graph/graph_solution.ipynb