LeetCode 2353. Design a Food Rating System Solution in Java, C++, Python & Go | Explanation + Code

Description

Design a food rating system that can do the following:

• Modify the rating of a food item listed in the system.
• Return the highest-rated food item for a type of cuisine in the system.

Implement the FoodRatings class:

• FoodRatings(String[] foods, String[] cuisines, int[] ratings) Initializes the system. The food items are described by foods, cuisines and ratings, all of which have a length of n.

  <ul>
  	<li><code>foods[i]</code> is the name of the <code>i<sup>th</sup></code> food,</li>
  	<li><code>cuisines[i]</code> is the type of cuisine of the <code>i<sup>th</sup></code> food, and</li>
  	<li><code>ratings[i]</code> is the initial rating of the <code>i<sup>th</sup></code> food.</li>
  </ul>
  </li>
  <li><code>void changeRating(String food, int newRating)</code> Changes the rating of the food item with the name <code>food</code>.</li>
  <li><code>String highestRated(String cuisine)</code> Returns the name of the food item that has the highest rating for the given type of <code>cuisine</code>. If there is a tie, return the item with the <strong>lexicographically smaller</strong> name.</li>
  

Note that a string x is lexicographically smaller than string y if x comes before y in dictionary order, that is, either x is a prefix of y, or if i is the first position such that x[i] != y[i], then x[i] comes before y[i] in alphabetic order.

 

Example 1:

Input
["FoodRatings", "highestRated", "highestRated", "changeRating", "highestRated", "changeRating", "highestRated"]
[[["kimchi", "miso", "sushi", "moussaka", "ramen", "bulgogi"], ["korean", "japanese", "japanese", "greek", "japanese", "korean"], [9, 12, 8, 15, 14, 7]], ["korean"], ["japanese"], ["sushi", 16], ["japanese"], ["ramen", 16], ["japanese"]]
Output
[null, "kimchi", "ramen", null, "sushi", null, "ramen"]

Explanation
FoodRatings foodRatings = new FoodRatings(["kimchi", "miso", "sushi", "moussaka", "ramen", "bulgogi"], ["korean", "japanese", "japanese", "greek", "japanese", "korean"], [9, 12, 8, 15, 14, 7]);
foodRatings.highestRated("korean"); // return "kimchi"
                                    // "kimchi" is the highest rated korean food with a rating of 9.
foodRatings.highestRated("japanese"); // return "ramen"
                                      // "ramen" is the highest rated japanese food with a rating of 14.
foodRatings.changeRating("sushi", 16); // "sushi" now has a rating of 16.
foodRatings.highestRated("japanese"); // return "sushi"
                                      // "sushi" is the highest rated japanese food with a rating of 16.
foodRatings.changeRating("ramen", 16); // "ramen" now has a rating of 16.
foodRatings.highestRated("japanese"); // return "ramen"
                                      // Both "sushi" and "ramen" have a rating of 16.
                                      // However, "ramen" is lexicographically smaller than "sushi".

 

Constraints:

• 1 <= n <= 2 * 104
• n == foods.length == cuisines.length == ratings.length
• 1 <= foods[i].length, cuisines[i].length <= 10
• foods[i], cuisines[i] consist of lowercase English letters.
• 1 <= ratings[i] <= 108
• All the strings in foods are distinct.
• food will be the name of a food item in the system across all calls to changeRating.
• cuisine will be a type of cuisine of at least one food item in the system across all calls to highestRated.
• At most 2 * 104 calls in total will be made to changeRating and highestRated.

Solutions

Solution 1: Hash Table + Ordered Set

We can use a hash table d to store the foods for each cuisine, where the key is the cuisine and the value is an ordered set. Each element in the ordered set is a tuple (rating, food), sorted by rating in descending order, and if the ratings are the same, sorted by food name in lexicographical order.

We can also use a hash table g to store the rating and cuisine for each food. That is, g[food] = (rating, cuisine).

In the constructor, we iterate through foods, cuisines, and ratings, storing the rating and cuisine for each food in d and g.

In the changeRating function, we first get the original rating oldRating and cuisine cuisine of the food food, then update the rating of g[food] to newRating, remove (oldRating, food) from d[cuisine], and add (newRating, food) to d[cuisine].

In the highestRated function, we directly return the food name of the first element in d[cuisine].

In terms of time complexity, the constructor has a time complexity of O(n log n), where n is the number of foods. The other operations have a time complexity of O(log n). The space complexity is O(n).

PythonJavaC++Go

class FoodRatings: def __init__(self, foods: List[str], cuisines: List[str], ratings: List[int]): self.d = defaultdict(SortedList) self.g = {} for food, cuisine, rating in zip(foods, cuisines, ratings): self.d[cuisine].add((-rating, food)) self.g[food] = (rating, cuisine) def changeRating(self, food: str, newRating: int) -> None: oldRating, cuisine = self.g[food] self.g[food] = (newRating, cuisine) self.d[cuisine].remove((-oldRating, food)) self.d[cuisine].add((-newRating, food)) def highestRated(self, cuisine: str) -> str: return self.d[cuisine][0][1] # Your FoodRatings object will be instantiated and called as such: # obj = FoodRatings(foods, cuisines, ratings) # obj.changeRating(food,newRating) # param_2 = obj.highestRated(cuisine)(code-box)

class FoodRatings { private Map<String, TreeSet<Pair<Integer, String>>> d = new HashMap<>(); private Map<String, Pair<Integer, String>> g = new HashMap<>(); private final Comparator<Pair<Integer, String>> cmp = (a, b) -> { if (!a.getKey().equals(b.getKey())) { return b.getKey().compareTo(a.getKey()); } return a.getValue().compareTo(b.getValue()); }; public FoodRatings(String[] foods, String[] cuisines, int[] ratings) { for (int i = 0; i < foods.length; ++i) { String food = foods[i], cuisine = cuisines[i]; int rating = ratings[i]; d.computeIfAbsent(cuisine, k -> new TreeSet<>(cmp)).add(new Pair<>(rating, food)); g.put(food, new Pair<>(rating, cuisine)); } } public void changeRating(String food, int newRating) { Pair<Integer, String> old = g.get(food); int oldRating = old.getKey(); String cuisine = old.getValue(); g.put(food, new Pair<>(newRating, cuisine)); d.get(cuisine).remove(new Pair<>(oldRating, food)); d.get(cuisine).add(new Pair<>(newRating, food)); } public String highestRated(String cuisine) { return d.get(cuisine).first().getValue(); } } /** * 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); */(code-box)

class FoodRatings { public: FoodRatings(vector<string>& foods, vector<string>& cuisines, vector<int>& ratings) { for (int i = 0; i < foods.size(); ++i) { string food = foods[i], cuisine = cuisines[i]; int rating = ratings[i]; d[cuisine].insert({-rating, food}); g[food] = {rating, cuisine}; } } void changeRating(string food, int newRating) { auto [oldRating, cuisine] = g[food]; g[food] = {newRating, cuisine}; d[cuisine].erase({-oldRating, food}); d[cuisine].insert({-newRating, food}); } string highestRated(string cuisine) { return d[cuisine].begin()->second; } private: unordered_map<string, set<pair<int, string>>> d; unordered_map<string, pair<int, string>> g; }; /** * 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); */(code-box)

import ( "github.com/emirpasic/gods/v2/trees/redblacktree" ) type pair struct { rating int food string } type FoodRatings struct { d map[string]*redblacktree.Tree[pair, struct{}] g map[string]pair } func Constructor(foods []string, cuisines []string, ratings []int) FoodRatings { d := make(map[string]*redblacktree.Tree[pair, struct{}]) g := make(map[string]pair) for i, food := range foods { rating, cuisine := ratings[i], cuisines[i] g[food] = pair{rating, cuisine} if d[cuisine] == nil { d[cuisine] = redblacktree.NewWith[pair, struct{}](func(a, b pair) int { return cmp.Or(b.rating-a.rating, strings.Compare(a.food, b.food)) }) } d[cuisine].Put(pair{rating, food}, struct{}{}) } return FoodRatings{d, g} } func (this *FoodRatings) ChangeRating(food string, newRating int) { p := this.g[food] t := this.d[p.food] t.Remove(pair{p.rating, food}) t.Put(pair{newRating, food}, struct{}{}) p.rating = newRating this.g[food] = p } func (this *FoodRatings) HighestRated(cuisine string) string { return this.d[cuisine].Left().Key.food } /** * Your FoodRatings object will be instantiated and called as such: * obj := Constructor(foods, cuisines, ratings); * obj.ChangeRating(food,newRating); * param_2 := obj.HighestRated(cuisine); */(code-box)