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.
  • 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.

 

Solutions

Solution: Priority Queue

• Time complexity: O(nlogn)
• Space complexity: O(n)

 

JavaScript

/**
 * @param {string[]} foods
 * @param {string[]} cuisines
 * @param {number[]} ratings
 */
const FoodRatings = function (foods, cuisines, ratings) {
  const n = foods.length;

  this.foodMap = new Map();
  this.cuisineMap = new Map();

  for (let index = 0; index < n; index++) {
    const food = foods[index];
    const cuisine = cuisines[index];
    const rating = ratings[index];

    this.foodMap.set(food, { cuisine, rating });

    if (!this.cuisineMap.has(cuisine)) {
      const heap = new PriorityQueue((a, b) => {
        return b.rating - a.rating || a.food.localeCompare(b.food);
      });

      this.cuisineMap.set(cuisine, heap);
    }

    this.cuisineMap.get(cuisine).enqueue({ food, rating });
  }
};

/**
 * @param {string} food
 * @param {number} newRating
 * @return {void}
 */
FoodRatings.prototype.changeRating = function (food, newRating) {
  const { cuisine } = this.foodMap.get(food);

  this.foodMap.set(food, { cuisine, rating: newRating });
  this.cuisineMap.get(cuisine).enqueue({ food, rating: newRating });
};

/**
 * @param {string} cuisine
 * @return {string}
 */
FoodRatings.prototype.highestRated = function (cuisine) {
  const heap = this.cuisineMap.get(cuisine);

  while (heap.front().rating !== this.foodMap.get(heap.front().food).rating) {
    heap.dequeue();
  }

  return heap.front().food;
};

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