102. Binary Tree Level Order Traversal.ipynb

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   "source": [
    "Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).\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 level order traversal as:\n",
    "[\n",
    "  [3],\n",
    "  [9,20],\n",
    "  [15,7]\n",
    "]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
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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"
   ]
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   "source": [
    "class Solution(object):\n",
    "    def levelOrder(self, root):\n",
    "        \"\"\"\n",
    "        :type root: TreeNode\n",
    "        :rtype: List[List[int]]\n",
    "        \"\"\"\n",
    "        if not root:\n",
    "            return []\n",
    "        ans=[]\n",
    "        queue=[root]\n",
    "        while len(queue)>0:\n",
    "            temp=[]\n",
    "            nextLayer=[]\n",
    "            for node in queue:\n",
    "                temp.append(node.val)\n",
    "                if node.left:\n",
    "                    nextLayer.append(node.left)\n",
    "                if node.right:\n",
    "                    nextLayer.append(node.right)\n",
    "            ans.append(temp)\n",
    "            queue=nextLayer\n",
    "        return ans\n",
    "                "
   ]
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  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {
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   "source": [
    "t1=TreeNode(2)\n",
    "t2=TreeNode(0)\n",
    "t3=TreeNode(3)\n",
    "t1.left=t2\n",
    "t1.right=t3\n",
    "t4=TreeNode(4)\n",
    "t5=TreeNode(5)\n",
    "t6=TreeNode(6)\n",
    "t2.left=t4\n",
    "t2.right=t5\n",
    "t4.left=t6"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {
    "collapsed": false
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   "outputs": [],
   "source": [
    "s=Solution()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[[2], [0, 3], [4, 5], [6]]"
      ]
     },
     "execution_count": 15,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "s.levelOrder(t1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "a=[1,2,3,4]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {
    "collapsed": false
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   "outputs": [
    {
     "data": {
      "text/plain": [
       "[1, 2, 3, 4]"
      ]
     },
     "execution_count": 11,
     "metadata": {},
     "output_type": "execute_result"
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   ],
   "source": [
    "a[::1]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[4, 3, 2, 1]"
      ]
     },
     "execution_count": 12,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a[::-1]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": []
  }
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