Python 5-line Straightforward Solution
\nclass Solution(object):\n    def longestWord(self, words):\n        """\n        :type words: List[str]\n        :rtype: str\n        """\n        valid = set
```\nclass Solution(object):\n    def longestWord(self, words):\n        """\n        :type words: List[str]\n        :rtype: str\n        """\n        valid = set([""])\n       \n        for word in sorted(words, key=lambda x: len(x)):\n           if word[:-1] in valid:\n                valid.add(word)\n\t\t\t\t\t\t\t\t\n        return max(sorted(valid), key=lambda x: len(x))\n```
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