1624. Largest Substring Between Two Equal Characters

class Solution {
public:
    int maxLengthBetweenEqualCharacters(const std::string& s) {
        std::vector<std::string> s1;
        for (char c : s) {
            s1.push_back(std::string(1, c));
        }

        for (int i = s1.size() - 1; i > 0; --i) {
            for (int j = 0; j + i < s1.size(); ++j) {
                if (s1[j] == s1[j + i]) {
                    return i - 1;
                }
            }
        }

        return -1;
    }
};