1392. Longest Happy Prefix

https://leetcode.com/problems/longest-happy-prefix

Description

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.

Example 3:

**Input:** s = "leetcodeleet"
**Output:** "leet"

Example 4:

**Input:** s = "a"
**Output:** ""

Constraints:

• 1 <= s.length <= 105

• s contains only lowercase English letters.

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