Clean Python 3, Set in two lines
Time: O(N)\nSpace: O(cities)\n\nclass Solution:\n    def destCity(self, paths: List[List[str]]) -> str:\n        A, B = map(set, zip(*paths))\n        return (B
Time: `O(N)`\nSpace: `O(cities)`\n```\nclass Solution:\n    def destCity(self, paths: List[List[str]]) -> str:\n        A, B = map(set, zip(*paths))\n        return (B - A).pop()\n```
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