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Java-based LeetCode algorithm problem solutions, regularly updated
1392\. Longest Happy Prefix
Hard
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 is also suffix is given by "l".
**Example 2:**
**Input:** s = "ababab"
**Output:** "abab"
**Explanation:** "abab" is the largest prefix which is also suffix. They can overlap in the original string.
**Constraints:**
* 1 <= s.length <= 105
* `s` contains only lowercase English letters.