1239. Maximum Length of a Concatenated String with Unique Characters.cpp

class Solution {
public:
    int maxLength(vector<string>& arr) {
        int res = 0;
        vector<bitset<26>> unique;
        for (auto s : arr){
            bitset<26> bin;
            for (char ch : s) bin.set(ch - 'a');
            if (bin.count() == s.size())
                unique.push_back(bin);
        }
        
        vector<bitset<26>> concat = {bitset<26>()};
        for (auto& u : unique)
            for (int i = concat.size() - 1; i >= 0; i--)
                if ((concat[i] & u).none()){
                    concat.push_back(concat[i] | u);
                    res = max(res, (int)(concat[i].count() + u.count()));
                }
        
        return res;
    }
};