[Swift]LeetCode1044. 最长重复子串 | Longest Duplicate Substring
原文：https://www.cnblogs.com/strengthen/p/10852170.html
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:
2 <= S.length <= 10^5Sconsists of lowercase English letters.
给出一个字符串 S，考虑其所有重复子串（S 的连续子串，出现两次或多次，可能会有重叠）。
返回任何具有最长可能长度的重复子串。（如果 S 不含重复子串，那么答案为 ""。）
示例 1：
输入："banana" 输出："ana"
示例 2：
输入："abcd" 输出：""
提示：
2 <= S.length <= 10^5S由小写英文字母组成。
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