string isValid(string s) {
    std::map<char, int> uniq;
    for (const char c : s) {
        uniq[c]++;
    }
    auto max = std::max_element(uniq.begin(), uniq.end(), 
        [](std::pair<char, int> el1, std::pair<char, int> el2){
             return el1.second < el2.second;
             });
    auto min = std::min_element(uniq.begin(), uniq.end(),
        [](std::pair<char, int> el1, std::pair<char, int> el2){
             return el1.second < el2.second;
             });

    if (std::all_of(uniq.begin(), uniq.end(), [max](const auto el){ return el.second == max->second; } )) {
        return "YES";
    }
    max->second--;
    if (std::all_of(uniq.begin(), uniq.end(), [min](const auto el){ return el.second == min->second; } )) {
        return "YES";
    }
    max->second++;
    min->second--;
    if (std::all_of(uniq.begin(), uniq.end(), [max](const auto el){ return el.second == max->second || el.second == 0; } )) {
        return "YES";
    }
    return "NO";
}