     "metadata": {},
     "source": [
      "## Test Cases\n",
      "\n",
      "* None tower(s)\n",
      "* 0 disks\n",
      "* 1 disk\n",
      "* 2 or more disks"
     ]
    },
    {
 
</s>
    "* None tower(s) -> Exception\n",
    "* 0 disks -> None\n",
     "metadata": {},
     "source": [
      "## Test Cases\n",
      "\n",
    "* None tower(s) -> Exception\n",
    "* 0 disks -> None\n",
    "* None tower(s) -> Exception\n",
    "* 0 disks -> None\n",
      "* 1 disk\n",
      "* 2 or more disks"
     ]
    },
    {
keep keep keep keep replace replace keep keep keep keep keep
 Update hanoi challenge (#121)

Update constraints and test cases.  Move implementation to a class.  Update tests.
recursion_dynamic/hanoi/hanoi_solution.ipynb