2353. Design a Food Rating System 

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 $\textit{d}$ 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 $(\textit{rating}, \textit{food})$, 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 $\textit{g}$ to store the rating and cuisine for each food. That is, $\textit{g}[\textit{food}] = (\textit{rating}, \textit{cuisine})$.

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

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

In the $\textit{highestRated}$ function, we directly return the food name of the first element in $\textit{d}[\textit{cuisine}]$.

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 $O(n)$.

Python3

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)

Java

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);
 */

C++

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);
 */

Go

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);
 */