Python BackTracking solution beats 100 %
\nclass Solution(object):\n    def __init__(self):\n        self.high = 0\n        \n    def maxLength(self, arr):\n        self.backtrack([],0, arr)\n        r
```\nclass Solution(object):\n    def __init__(self):\n        self.high = 0\n        \n    def maxLength(self, arr):\n        self.backtrack([],0, arr)\n        return self.high\n    \n    def backtrack(self,res, start, arr):\n        self.high = max(self.high, len("".join(res)))\n        \n        for i in range(start, len(arr)):\n            res.append(arr[i])\n            temp = "".join(res)\n            if len(set(temp)) == len(temp):\n                self.backtrack(res, i+1, arr )\n            res.pop()\n```
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