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    "https://leetcode.com/problems/flatten-a-multilevel-doubly-linked-list\n",
    "\n",
    "\n",
    "Runtime: 48 ms, faster than 22.06% of Python3 online submissions for Flatten a Multilevel Doubly Linked List.\n",
    "Memory Usage: 15.1 MB, less than 29.91% of Python3 online submissions for Flatten a Multilevel Doubly Linked List.\n",
    "\n",
    "\n",
    "```python\n",
    "class Solution:\n",
    "    def flatten(self, head: 'Node') -> 'Node':\n",
    "        #11:19\n",
    "        l = [head]\n",
    "        newL = []\n",
    "        while len(l):\n",
    "            node = l[0]\n",
    "            l = l[1:]\n",
    "            if node:\n",
    "                if node.next != None:\n",
    "                    l.insert(0, node.next)\n",
    "                if node.child != None:\n",
    "                    l.insert(0, node.child)\n",
    "                newL.append(node)\n",
    "        for i, v in enumerate(newL):\n",
    "            #print(v.val)\n",
    "            if i == 0:\n",
    "                newL[i].prev = None\n",
    "                newL[i].next = newL[i+1]\n",
    "            elif i == len(newL) - 1:\n",
    "                newL[i].prev = newL[i-1]\n",
    "                newL[i].next = None\n",
    "            else:\n",
    "                newL[i].prev = newL[i-1]\n",
    "                newL[i].next = newL[i+1]\n",
    "            newL[i].child = None\n",
    "        if len(newL):\n",
    "            return newL[0]\n",
    "        else:\n",
    "            return head\n",
    "        #11:21 done; 11:32 debug            \n",
    "```"
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