      "*Problem statements are sometimes ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
      "\n",
      "* Is this a singly or doubly linked list?\n",
      "    * Singly\n",
      "* Can you insert NULL values in the list?\n",
      "    * No\n",
      "* Can you use additional data structures?\n",
      "    * Implement both solutions\n",
      "* Can we assume we already have a linked list class that can be used for this problem?\n",
      "    * Yes"
 
</s> remove     "* Space: O(m) where m is the number of values in the hash map\n",
 </s> add     "* Space: O(n)\n", </s> remove     "* Space: In-place\n",
 </s> add     "* Space: O(1)\n", </s> remove     "* Can you insert NULL values in the list?\n",
 </s> add     "* Can you insert None values in the list?\n",
    "* Can you insert None values in the list?\n",
      "*Problem statements are sometimes ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
      "\n",
      "* Is this a singly or doubly linked list?\n",
      "    * Singly\n",
    "* Can you insert None values in the list?\n",
      "    * No\n",
      "* Can you use additional data structures?\n",
      "    * Implement both solutions\n",
      "* Can we assume we already have a linked list class that can be used for this problem?\n",
      "    * Yes"
keep keep keep keep replace keep keep keep keep keep
 Tweaked remove duplicates challenge algorithm discussion. 
linked_lists/remove_duplicates/remove_duplicates_challenge.ipynb