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2353 Design a Food Rating System Medium

Problem:

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.
    • foods[i] is the name of the ith food,
    • cuisines[i] is the type of cuisine of the ith food, and
    • ratings[i] is the initial rating of the ith food.
  • void changeRating(String food, int newRating) Changes the rating of the food item with the name food.
  • String highestRated(String cuisine) Returns the name of the food item that has the highest rating for the given type of cuisine. If there is a tie, return the item with the lexicographically smaller name.

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.

Problem Analysis:

It uses three data structures to organize the information:

  1. self.cuisines_food: A defaultdict where the keys are cuisines, and the values are SortedSets containing tuples of the form (-rating, food). The SortedSet is used to keep the foods sorted by their ratings in descending order.

  2. self.cuisines: A dictionary mapping each food to its corresponding cuisine.

  3. self.ratings: A dictionary mapping each food to its rating.

  • Let n be the number of foods.
  • The constructor (__init__) has a time complexity of O(nlogn) because, for each food, it performs operations like adding to SortedSets and populating dictionaries.
  • The changeRating method has a time complexity of O(logn) because it involves updating the SortedSet for a cuisine.
  • The highestRated method has a time complexity of O(1) as it directly retrieves the highest-rated food from the SortedSet.
  • The space complexity is O(n) due to the storage of cuisines, ratings, and SortedSets.

Solutions:

from sortedcontainers import SortedSet

class FoodRatings:

    def __init__(self, foods: List[str], cuisines: List[str], ratings: List[int]):
        self.cuisines_food = defaultdict(SortedSet) # {cuisine : (rating, food)}
        self.cuisines = {} # {food:  cuisine}
        self.ratings = {} # {food: ratings}

        for i in range(len(foods)):
            # sort in desc
            self.cuisines_food[cuisines[i]].add((-ratings[i], foods[i]))
            self.cuisines[foods[i]] = cuisines[i]
            self.ratings[foods[i]] = ratings[i]

    def changeRating(self, food: str, newRating: int) -> None:
        # get original cuisine, rating
        c = self.cuisines[food]
        r = self.ratings[food]

        self.cuisines_food[c].remove((-r, food))
        self.cuisines_food[c].add((-newRating, food))
        self.ratings[food] = newRating

    def highestRated(self, cuisine: str) -> str:
        return self.cuisines_food[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)

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