20. 有效的括号.ipynb

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       "True"
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    "class Solution:\n",
    "    def isValid(self, s: str) -> bool:\n",
    "        i = 0\n",
    "        while i < len(s)-1:\n",
    "            if (s[i] == '[' and s[i+1] == ']') or (s[i] == '(' and s[i+1] == ')' or s[i] == '{' and s[i+1] == '}'):\n",
    "                if i+2 < len(s):\n",
    "                    s = s[:i]+s[i+2:] \n",
    "                else:\n",
    "                    s = s[:i]\n",
    "                i -= 1\n",
    "            else:\n",
    "                i += 1\n",
    "        return len(s)==0\n",
    "s = Solution()\n",
    "s.isValid('')"
   ]
  }
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