2982 - Find Longest Special Substring That Occurs Thrice II\.

Medium

You are given a string s that consists of lowercase English letters.

A string is called special if it is made up of only a single character. For example, the string "abc" is not special, whereas the strings "ddd", "zz", and "f" are special.

Return the length of the longest special substring of s which occurs at least thrice, or -1 if no special substring occurs at least thrice.

A substring is a contiguous non-empty sequence of characters within a string.

Example 1:

Input: s = "aaaa"

Output: 2

Explanation: The longest special substring which occurs thrice is "aa": substrings "<ins> aa </ins>aa", "a<ins> aa </ins>a", and "aa<ins> aa </ins>".

It can be shown that the maximum length achievable is 2.

Example 2:

Input: s = "abcdef"

Output: -1

Explanation: There exists no special substring which occurs at least thrice. Hence return -1.

Example 3:

Input: s = "abcaba"

Output: 1

Explanation: The longest special substring which occurs thrice is "a": substrings "<ins> a </ins>bcaba", "abc<ins> a </ins>ba", and "abcab<ins> a </ins>".

It can be shown that the maximum length achievable is 1.

Constraints:

• <code>3 <= s.length <= 5 * 10⁵</code>

• s consists of only lowercase English letters.