      "    * value: node\n",
      "\n",
      "#### add_node\n",
      "\n",
      "* Create a node with the input id\n",
      "* Add the newly created node to the list of nodes\n",
      "\n",
      "Complexity:\n",
      "* Time: O(1)\n",
      "* Space: O(1)\n",
      "\n",
 
</s> remove     "    * key: node id\n",
    "    * value: node\n",
 </s> add  </s> remove     "* If the source node is not in the list of nodes, add it\n",
    "* If the dest node is not in the list of nodes, add it\n",
 </s> add     "* If the source node is not in the collection of nodes, add it\n",
    "* If the dest node is not in the collection of nodes, add it\n", </s> remove     "* Add the neighbor as a key and the weight as the value to `adjacent`\n",
 </s> add     "* If the neighbor doesn't already exist as an adjacent node\n",
    "    * Update the adjancet nodes and edge weights\n",
    "    * Increment the neighbor's incoming edge count\n",
    "\n",
    "Complexity:\n",
    "* Time: O(1)\n",
    "* Space: O(1)\n",
    "\n",
    "#### remove_neighhbor\n",
    "\n",
    "* If the neighbor exists as an adjacent node\n",
    "    * Decrement the neighbor's incoming edge count\n",
    "    * Remove the neighbor as an adjacent node\n", </s> remove     "* adjacent\n",
    "    * key: node\n",
    "    * value: weight\n",
 </s> add     "* incoming edge count (useful for algorithms such as topological sort)\n",
    "* adjacent nodes and edge weights\n",
    "* If node already exists, return it\n",
    "* Create a node with the given id\n",
    "* Add the newly created node to the collection of nodes\n",
      "    * value: node\n",
      "\n",
      "#### add_node\n",
      "\n",
    "* If node already exists, return it\n",
    "* Create a node with the given id\n",
    "* Add the newly created node to the collection of nodes\n",
    "* If node already exists, return it\n",
    "* Create a node with the given id\n",
    "* Add the newly created node to the collection of nodes\n",
      "\n",
      "Complexity:\n",
      "* Time: O(1)\n",
      "* Space: O(1)\n",
      "\n",
keep keep keep keep replace replace keep keep keep keep keep
 Rework graph challenge and solution (#90) 
graphs_trees/graph/graph_solution.ipynb