1392. Longest Happy Prefix

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A string is called a happy prefix if is a non-empty prefix which is also a suffix (excluding itself). Given a string s, return the longest happy prefix of s. Return an empty string "" if no such prefix exists. Example 1: Input: s = "level" Output: "l" Explanation: s contains 4 prefix excluding itself ("l", "le", "lev", "leve"), and suffix ("l", "el", "vel", "evel"). The largest prefix which i

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