Problem

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.

Examples

Example 1:

Input: s = "aaaa"
Output: 2
Explanation: The longest special substring which occurs thrice is "aa": substrings "a̲a̲aa", "a a̲a̲a", and "aa a̲a̲".
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 "a̲bcaba", "abca̲ba", and "abcaba̲".
It can be shown that the maximum length achievable is 1.

Constraints:

  • 3 <= s.length <= 5 * 10^5
  • s consists of only lowercase English letters.

Solution

This solutions to this problem are already covered here - Find Longest Special Substring That Occurs Thrice 1. This problem is similar to previous problem, with the difference in terms of constraint. Here the string length can be uptill 5*10^5, which is much larger than previous problem, where the max length of string was 50.