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 <= 10^5scontains only lowercase English letters.