Day 19 of June LeetCode Challenge

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: "banana"
Output: "ana"

Example 2:

Input: "abcd"
Output: ""

Note:

1. 2 <= S.length <= 10^5
2. S consists of lowercase English letters.