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    "https://leetcode.com/problems/generate-parentheses\n",
    "\n",
    "\n",
    "Runtime: 368 ms, faster than 5.09% of Python3 online submissions for Generate Parentheses.\n",
    "Memory Usage: 14.5 MB, less than 89.25% of Python3 online submissions for Generate Parentheses.\n",
    "\n",
    "\n",
    "```python\n",
    "class Solution:\n",
    "    def __init__(self):\n",
    "        self.doneLevelDict = {}\n",
    "    \n",
    "    def generateParenthesis(self, n: int) -> List[str]:\n",
    "        #2022.1.7 7:50\n",
    "        n *= 2\n",
    "        \n",
    "        if n in self.doneLevelDict:\n",
    "            return self.doneLevelDict[n]\n",
    "        \n",
    "        def validator(string):\n",
    "            if len(string) == 0:\n",
    "                return False\n",
    "            \n",
    "            for i in range(n // 2):\n",
    "                string = string.replace(\"()\", \"\", 1)\n",
    "                i += 1\n",
    "                if i != n//2:\n",
    "                    if string == \"\":\n",
    "                        return False\n",
    "                else:\n",
    "                    if string == \"\":\n",
    "                        return True\n",
    "        \n",
    "        tempList = []\n",
    "        def generate(string):\n",
    "            if len(string) == n:\n",
    "                return\n",
    "            else:\n",
    "                A = string + \"(\"\n",
    "                B = string + \")\"\n",
    "                if validator(A):\n",
    "                    tempList.append(A)\n",
    "                if validator(B):\n",
    "                    tempList.append(B)\n",
    "                generate(A)\n",
    "                generate(B)\n",
    "        \n",
    "        generate(\"\")\n",
    "        self.doneLevelDict[n] = tempList\n",
    "        return tempList\n",
    "        #2022.1.7 8:06\n",
    "        #debug until 8:10\n",
    "```"
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