{ "data": { "question": { "questionId": "1508", "questionFrontendId": "1392", "categoryTitle": "Algorithms", "boundTopicId": 160209, "title": "Longest Happy Prefix", "titleSlug": "longest-happy-prefix", "content": "

A string is called a happy prefix if is a non-empty prefix which is also a suffix (excluding itself).

\n\n

Given a string s, return the longest happy prefix of s. Return an empty string "" if no such prefix exists.

\n\n

 

\n

Example 1:

\n\n
\nInput: s = "level"\nOutput: "l"\nExplanation: s contains 4 prefix excluding itself ("l", "le", "lev", "leve"), and suffix ("l", "el", "vel", "evel"). The largest prefix which is also suffix is given by "l".\n
\n\n

Example 2:

\n\n
\nInput: s = "ababab"\nOutput: "abab"\nExplanation: "abab" is the largest prefix which is also suffix. They can overlap in the original string.\n
\n\n

 

\n

Constraints:

\n\n\n", "translatedTitle": "最长快乐前缀", "translatedContent": "

「快乐前缀」 是在原字符串中既是 非空 前缀也是后缀（不包括原字符串自身）的字符串。

\n\n

给你一个字符串 s，请你返回它的 最长快乐前缀。如果不存在满足题意的前缀，则返回一个空字符串 \"\" 。

\n\n

 

\n\n

示例 1：

\n\n
\n输入：s = \"level\"\n输出：\"l\"\n解释：不包括 s 自己，一共有 4 个前缀（\"l\", \"le\", \"lev\", \"leve\"）和 4 个后缀（\"l\", \"el\", \"vel\", \"evel\"）。最长的既是前缀也是后缀的字符串是 \"l\" 。\n
\n\n

示例 2：

\n\n
\n输入：s = \"ababab\"\n输出：\"abab\"\n解释：\"abab\" 是最长的既是前缀也是后缀的字符串。题目允许前后缀在原字符串中重叠。\n
\n\n

 

\n\n

提示：

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