algorithms/326-power-of-three.ipynb

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    "### [3的幂](https://leetcode-cn.com/problems/power-of-three/)\n",
    "\n",
    "给定一个整数，写一个函数来判断它是否是 3 的幂次方。如果是，返回 true ；否则，返回 false 。\n",
    "\n",
    "整数 n 是 3 的幂次方需满足：存在整数 x 使得 n == 3x\n",
    "\n",
    "#### 示例 1：\n",
    "```\n",
    "输入：n = 27\n",
    "输出：true\n",
    "```\n",
    "\n",
    "#### 示例 2：\n",
    "```\n",
    "输入：n = 0\n",
    "输出：false\n",
    "```\n",
    "\n",
    "#### 示例 3：\n",
    "```\n",
    "输入：n = 9\n",
    "输出：true\n",
    "```\n",
    "\n",
    "#### 示例 4：\n",
    "```\n",
    "输入：n = 45\n",
    "输出：false\n",
    "```\n",
    "\n",
    "#### 提示：\n",
    "- $-2^{31} <= n <= 2^{31} - 1$"
   ]
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    "def isPowerOfThree(n: int) -> bool:\n",
    "    if n < 3:\n",
    "        return n == 1\n",
    "    else:\n",
    "        return n % 3 == 0 and isPowerOfThree(n // 3)"
   ]
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       "True"
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   "source": [
    "isPowerOfThree(27)"
   ]
  }
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