Longest Proper Prefix That Is Also a Suffix

### Problem Return the longest nonempty prefix of s that is also a suffix, excluding s itself. The prefix and suffix occurrences may overlap. Return the empty string when no such nonempty proper prefix exists. ```cpp class Solution { public: string longestPrefix(string s); }; ``` ### Examples **Example 1:** ```text Input: s = "aaaa" Output: "aaa" Explanation: The length3 prefix and suffix overlap and are equal; length4 is forbidden because it is the whole string. ``` **Example 2:** ```text Input: s = "abcd" Output: "" Explanation: No nonempty proper prefix matches a suffix. ``` ### Constraints - s has length 1 to 100000. - Every character is a lowercase English letter. ### Contract considerations The result is uniquely determined by its maximal length. ```hint Read the boundary condition Check overlapping prefix and suffix occurrences, a one-letter string, and the exclusion of the entire string. ``` ### Boundary reminders The result is uniquely determined by its maximal length.