      "\n",
      "* Empty list -> None\n",
      "* Not a circular linked list -> None\n",
      "    * One element\n",
      "    * Two elements\n",
      "    * Three or more elements\n",
      "* General case"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
 
</s> remove     "    * Two elements\n",
    "    * Three or more elements\n",
    "* General case"
 </s> add     "    * Two or more elements\n",
    "* Circular linked list general case" </s> remove     "        * If j's next is NULL, we do not have a circular list\n",
 </s> add     "        * If j's next is None, we do not have a circular list\n", </s> remove     "* Space: In-place"
 </s> add     "* Space: O(1)"
    "    * Two or more elements\n",
    "* Circular linked list general case"
      "\n",
      "* Empty list -> None\n",
      "* Not a circular linked list -> None\n",
      "    * One element\n",
    "    * Two or more elements\n",
    "* Circular linked list general case"
    "    * Two or more elements\n",
    "* Circular linked list general case"
    "    * Two or more elements\n",
    "* Circular linked list general case"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
keep keep keep keep replace replace replace keep keep keep keep keep
 Tweaked find loop start challenge test cases and algorith discussion. 
linked_lists/find_loop_start/find_loop_start_challenge.ipynb