107. Binary Tree Level Order Traversal II.ipynb

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    "Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).\n",
    "\n",
    "For example:\n",
    "Given binary tree [3,9,20,null,null,15,7],\n",
    "    3\n",
    "   / \\\n",
    "  9  20\n",
    "    /  \\\n",
    "   15   7\n",
    "return its bottom-up level order traversal as:\n",
    "[\n",
    "  [15,7],\n",
    "  [9,20],\n",
    "  [3]\n",
    "]"
   ]
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    "n1=TreeNode(3)\n",
    "n2=TreeNode(9)\n",
    "n3=TreeNode(20)\n",
    "n4=TreeNode(15)\n",
    "n5=TreeNode(7)\n",
    "n6=TreeNode(6)\n",
    "n1.left=n2\n",
    "n1.right=n3\n",
    "n3.left=n4\n",
    "n3.right=n5\n",
    "n4.left=n6"
   ]
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   "source": [
    "class TreeNode(object):\n",
    "    def __init__(self,x):\n",
    "        self.val=x\n",
    "        self.left=None\n",
    "        self.right=None\n",
    "class Solution(object):\n",
    "    def levelOrderBottom(self, root):\n",
    "        \"\"\"\n",
    "        :type root: TreeNode\n",
    "        :rtype: List[List[int]]\n",
    "        \"\"\"\n",
    "        self.res=[]\n",
    "        \n",
    "        self.dfs(root,0)\n",
    "        return self.res\n",
    "    def dfs(self,root,level):\n",
    "        if not root:\n",
    "            return\n",
    "        if len(self.res)<level+1:\n",
    "            self.res.insert(0,[])\n",
    "       \n",
    "        self.res[-(level+1)].append(root.val)\n",
    "        self.dfs(root.left,level+1)\n",
    "        self.dfs(root.right,level+1)\n",
    "        \n",
    "        \n",
    "        "
   ]
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   "source": [
    "s=Solution()\n"
   ]
  },
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   "outputs": [
    {
     "data": {
      "text/plain": [
       "[[6], [15, 7], [9, 20], [3]]"
      ]
     },
     "execution_count": 55,
     "metadata": {},
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   ],
   "source": [
    "s.levelOrderBottom(n1)"
   ]
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       "[[], [2, 3]]"
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    "a[0].append(10)"
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       "[[10], [2, 3]]"
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   "source": [
    "def levelOrderBottom1(self, root):\n",
    "    res = []\n",
    "    self.dfs(root, 0, res)\n",
    "    return res\n",
    "\n",
    "def dfs(self, root, level, res):\n",
    "    if root:\n",
    "        if len(res) < level + 1:\n",
    "            res.insert(0, [])\n",
    "        res[-(level+1)].append(root.val)\n",
    "        self.dfs(root.left, level+1, res)\n",
    "        self.dfs(root.right, level+1, res)"
   ]
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