819.cpp

// hash.cpp
class Solution {
public:
  string mostCommonWord(string paragraph, vector<string> &banned) {
    unordered_map<string, int> wordmap;
    transform(paragraph.begin(), paragraph.end(), paragraph.begin(),
              [](char &ch) -> char {
                switch (ch) {
                case '!':
                case '?':
                case '\'':
                case ',':
                case ';':
                case '.':
                  return ' ';
                }
                return tolower(ch);
              });
    unordered_set<string> bannedSet(banned.begin(), banned.end());
    stringstream ss(paragraph);
    string str;
    while (!ss.eof()) {
      ss >> str;
      if (bannedSet.find(str) == bannedSet.end())
        ++wordmap[str];
    }
    return max_element(wordmap.begin(), wordmap.end(),
                       [](const pair<const string, int> &a,
                          const pair<const string, int> &b) {
                         return a.second < b.second;
                       })
        ->first;
  }
};