Given a string s, return the length of the longest substring between two equal characters, excluding the two characters. If there is no such substring return -1. A substring is a contiguous sequence of characters within a string. Example 1: Input: s = "aa" Output: 0 Explanation: The optimal substring here is an empty substring between the two 'a's. Example 2: Input: s = "abca" Output: 2 Explanation: The optimal substring here is "bc". Example 3: Input: s = "cbzxy" Output: -1 Explanation: There are no characters that appear twice in s. Example 4: Input: s = "cabbac" Output: 4 Explanation: The optimal substring here is "abba". Other non-optimal substrings include "bb" and "". Constraints: 1 <= s.length <= 300 s contains only lowercase English letters.