1624. Largest Substring Between Two Equal Characters - Explanation

class Solution:
    def maxLengthBetweenEqualCharacters(self, s: str) -> int:
        n = len(s)
        res = -1

        for i in range(n):
            for j in range(i + 1, n):
                if s[i] == s[j]:
                    res = max(res, j - i - 1)
        return res

class Solution:
    def maxLengthBetweenEqualCharacters(self, s: str) -> int:
        res = -1
        firstIdx = {}
        lastIdx = {}

        for i, c in enumerate(s):
            if c not in firstIdx:
                firstIdx[c] = i
            else:
                lastIdx[c] = i

        for c in lastIdx:
            res = max(res, lastIdx[c] - firstIdx[c] - 1)

        return res

class Solution:
    def maxLengthBetweenEqualCharacters(self, s: str) -> int:
        char_index = {}  # char -> first index
        res = -1

        for i, c in enumerate(s):
            if c in char_index:
                res = max(res, i - char_index[c] - 1)
            else:
                char_index[c] = i

        return res

class Solution:
    def maxLengthBetweenEqualCharacters(self, s: str) -> int:
        firstIdx = [-1] * 26
        res = -1

        for i, c in enumerate(s):
            j = ord(c) - ord('a')
            if firstIdx[j] != -1:
                res = max(res, i - firstIdx[j] - 1)
            else:
                firstIdx[j] = i

        return res