      "        * Add node's value to the hash map\n",
      "\n",
      "Complexity:\n",
      "* Time: O(n)\n",
      "* Space: O(n)\n",
      "\n",
      "Note:\n",
      "* Deletion requires two pointers, one to the previous node and one to the current node"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
 
</s> remove     "* Deletion requires two pointers, one to the previous node and one to the current node\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     "* Can you use additional data structures?\n",
    "    * Implement both solutions\n",
 </s> add 
    "* Space: O(n)"
      "        * Add node's value to the hash map\n",
      "\n",
      "Complexity:\n",
      "* Time: O(n)\n",
    "* Space: O(n)"
    "* Space: O(n)"
    "* Space: O(n)"
    "* Space: O(n)"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
keep keep keep keep replace replace replace replace keep keep keep keep keep
 Polish remove duplicates challenge and solution

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