      "* Can you insert None values in the list?\n",
      "    * No\n",
      "* Can we assume we already have a linked list class that can be used for this problem?\n",
      "    * Yes"
     ]
    },
    {
 
</s> remove     "* Can you use additional data structures?\n",
    "    * Implement both solutions\n",
 </s> add  </s> remove     "* Can you use additional data structures?\n",
    "    * Implement both solutions\n",
 </s> add  </s> remove     "        * If the node's value is in the hash map\n",
    "            * Delete the node\n",
    "        * Else\n",
    "            * Add node's value to the hash map\n",
 </s> add     "        * Delete nodes that match current node\n", </s> remove     "* Space: O(n)\n",
    "\n",
    "Note:\n",
    "* Deletion requires two pointers, one to the previous node and one to the current node"
 </s> add     "* Space: O(n)"
    "    * Yes\n",
    "* Can we use additional data structures?\n",
    "    * Implement both solutions\n",
    "* Can we assume this fits in memory?\n",
      "* Can you insert None values in the list?\n",
      "    * No\n",
      "* Can we assume we already have a linked list class that can be used for this problem?\n",
    "    * Yes\n",
    "* Can we use additional data structures?\n",
    "    * Implement both solutions\n",
    "* Can we assume this fits in memory?\n",
      "    * Yes"
     ]
    },
    {
keep keep add keep keep keep keep
 Polish remove duplicates challenge and solution

Update constraints and algorithm discussion. 
linked_lists/remove_duplicates/remove_duplicates_solution.ipynb