用了三个Hashtable…

1. 菜名 -> 菜系
2. 菜系 -> Treemap
3. 菜名 -> 所在Treemap中的迭代器

每个菜系用一个TreeSet来保存从高到低的菜色排名，查询的时候只要拿出第一个就好了。

修改的时候，拿出迭代器，删除原来的评分，再把新的评分加入（别忘了更新迭代器）

时间复杂度：构造O(nlogn)，修改O(logn)，查询O(1)

空间复杂度：O(n)

class FoodRatings {
public:
  FoodRatings(vector<string>& foods, vector<string>& cuisines, vector<int>& ratings) {
    const int n = foods.size();
    for (int i = 0; i < n; ++i) {
      n_[foods[i]] = cuisines[i];
      m_[foods[i]] = c_[cuisines[i]].emplace(-ratings[i], foods[i]).first;
    }
  }
  
  void changeRating(string food, int newRating) {
    const string& cuisine = n_[food];
    c_[cuisine].erase(m_[food]);
    m_[food] = c_[cuisine].emplace(-newRating, food).first;
  }
  
  string highestRated(string cuisine) {
    return begin(c_[cuisine])->second;
  }
private:
  unordered_map<string, set<pair<int, string>>> c_; // cuisine -> {{-rating, name}}
  unordered_map<string, string> n_; // food -> cuisine  
  unordered_map<string, set<pair<int, string>>::iterator> m_; // food -> set iterator
};

/**
 * Your FoodRatings object will be instantiated and called as such:
 * FoodRatings* obj = new FoodRatings(foods, cuisines, ratings);
 * obj->changeRating(food,newRating);
 * string param_2 = obj->highestRated(cuisine);
 */

The post 花花酱 LeetCode 2353. Design a Food Rating System appeared first on Huahua's Tech Road.