17. 电话号码的字母组合.ipynb

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     "data": {
      "text/plain": [
       "['ad', 'ae', 'af', 'bd', 'be', 'bf', 'cd', 'ce', 'cf']"
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    "class Solution:\n",
    "    def letterCombinations(self, digits: str) -> [str]:\n",
    "        dic = {\n",
    "            '2': 'abc',\n",
    "            '3': 'def',\n",
    "            '4': 'ghi',\n",
    "            '5': 'jkl',\n",
    "            '6': 'mno',\n",
    "            '7': 'pqrs',\n",
    "            '8': 'tuv',\n",
    "            '9': 'wxyz',\n",
    "        }\n",
    "        def backtrack(string, next_digits):\n",
    "            if len(next_digits) == 0:\n",
    "                if len(string) == 0:\n",
    "                    return\n",
    "                res.append(string)\n",
    "            else:\n",
    "                for s in dic[next_digits[0]]:\n",
    "                    backtrack(string+s, next_digits[1:])\n",
    "        res = []\n",
    "        backtrack('',digits)\n",
    "        \n",
    "        return res\n",
    "s = Solution()\n",
    "s.letterCombinations('23')\n",
    "        \n",
    "        "
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