318.cpp

// higher-efficient.cpp
class Solution {
public:
  int maxProduct(vector<string> &words) {
    int len = 0;
    vector<int> comp(words.size(), 0);
    for (int i = 0; i < words.size(); ++i) {
      string &str = words[i];
      for (int j = 0; j < str.size(); ++j)
        comp[i] |= 1 << (str[j] - 'a');
    }
    for (int i = 0; i < words.size(); ++i)
      for (int j = i + 1; j < words.size(); ++j)
        if ((comp[i] & comp[j]) == 0)
          len = max(len, (int)(words[i].size() * words[j].size()));
    return len;
  }
};
// lower-efficient.cpp
class Solution2 {
public:
  int maxProduct(vector<string> &words) {
    int len = 0;
    for (int i = 0; i < words.size(); ++i) {
      unordered_set<char> hashset(words[i].begin(), words[i].end());
      for (int j = i + 1; j < words.size(); ++j) {
        bool withoutCommon = true;
        for (int k = 0; k < words[j].size(); ++k)
          if (hashset.find(words[j][k]) != hashset.end()) {
            withoutCommon = false;
            break;
          }
        len = withoutCommon ? max(len, (int)(words[i].size() * words[j].size()))
                            : len;
      }
    }
    return len;
  }
};