【leetcode】1624. Largest Substring Between Two Equal Characters

题目如下：

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.

解题思路：遍历s，记录每个字符最早出现的位置，遇到相同的字符的时候，找出第一个字符出现的位置，两者之间即为符合条件的一个子串，求出最大值即可。

代码如下：

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