題目如下：

Given a strings, returnthe length of the longest substring between two equal characters, excluding the two characters.If there is no such substring return-1.

Asubstringis 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
• scontains only lowercase English letters.

解題思路：遍歷s，記錄每個字元最早出現的位置，遇到相同的字元的時候，找出第一個字元出現的位置，兩者之間即為符合條件的一個子串，求出最大值即可。

程式碼如下：

class Solution(object):
    def maxLengthBetweenEqualCharacters(self, s):
        """
        :type s: str
        :rtype: int
        """
 

        dic_last_inx = {}
        res = -1
        for i in range(len(s)):
            if s[i] not in dic_last_inx:
                dic_last_inx[s[i]] = i
            else:
                res = max(res,i - dic_last_inx[s[i]] - 1)
        return res