Given a string `s`, consider all duplicated substrings: (contiguous) substrings of s that occur 2 or more times. The occurrences may overlap.

Return any duplicated substring that has the longest possible length. If `s` does not have a duplicated substring, the answer is `""`.

Example 1:

    Input: s = "banana"
    Output: "ana"

Example 2:

    Input: s = "abcd"
    Output: ""

Constraints:

- `2 <= s.length <= 3 * 104`
- `s` consists of lowercase English letters.