2429. Design A Food Rating System¶

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2429. Design a Food Rating System

Medium

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.

Solution¶

class FoodRatings {
    private HashMap<String, TreeSet<Pair>> map;
    private HashMap<String, ArrayList<String>> foodMap; // currentFood is present in which of the cousines;
    private HashMap<String, Integer> ratingMap; // Currently what is the rating of each food;
    static class Pair {
        String food;
        int rating;
        public Pair(String food, int rating) {
            this.food = food;
            this.rating = rating;
        }
        @Override
        public String toString() {
            return "(" + food + " " + rating + ")";
        }
        @Override
        public boolean equals(Object obj) {
            if (this == obj)
                return true;
            if (obj == null || getClass() != obj.getClass())
                return false;
            Pair current = (Pair)(obj);
            return current.food.equals(food) && current.rating == rating;
        }
        @Override
        public int hashCode() {
            return Objects.hash(food, rating);
        }
    }

    static class customSort implements Comparator<Pair> {
        @Override
        public int compare(Pair first, Pair second) {
            int op1 = Integer.compare(second.rating, first.rating);
            if (op1 != 0)
                return op1;
            return first.food.compareTo(second.food);
        }
    }

    public FoodRatings(String[] foods, String[] cuisines, int[] ratings) {
        int n = foods.length;
        map = new HashMap<>();
        foodMap = new HashMap<>();
        ratingMap = new HashMap<>();
        for (int i = 0; i < n; i++) {
            String type = cuisines[i], food = foods[i];
            if (!map.containsKey(type)) 
                map.put(type, new TreeSet<Pair>(new customSort()));
            map.get(type).add(new Pair(foods[i], ratings[i]));
            if (!foodMap.containsKey(food))
                foodMap.put(food, new ArrayList<>());
            foodMap.get(food).add(cuisines[i]);
            ratingMap.put(foods[i], ratings[i]);
        } 
    }

    public void changeRating(String food, int newRating) {
        ArrayList<String> ids = new ArrayList<>();
        ids = foodMap.get(food);
        for (int i = 0; i < ids.size(); i++) {
            TreeSet<Pair> currCuines = new TreeSet<>();
            currCuines = map.get(ids.get(i));
            //update the food and its rating;
            int currRating = ratingMap.get(food);
            currCuines.remove(new Pair(food, currRating));
            currCuines.add(new Pair(food, newRating));
            map.put(ids.get(i), currCuines);
            ratingMap.put(food, newRating);
        } 
    }

    public String highestRated(String cuisine) {
        TreeSet<Pair> curr = map.get(cuisine);
        return curr.first().food; 
    }
}

/**
 * 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);
 */

Complexity Analysis¶

• Time Complexity: O(?)
• Space Complexity: O(?)

Approach¶

Detailed explanation of the approach will be added here