Create 2353-design-a-food-rating-system.java

Author: sanajitjana

Medium/2353-design-a-food-rating-system.java

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+/*
+Problem: Design a Food Rating System
+LeetCode Link: https://leetcode.com/problems/design-a-food-rating-system/
+
+Approach:
+We need a data structure to:
+- Quickly find the highest-rated food in a given cuisine.
+- Efficiently update the rating of a food.
+
+Use three maps:
+1. foodCuisines: Maps food → cuisine.
+2. foodRating: Maps food → rating.
+3. cuisinesRatingFood: Maps cuisine → TreeSet of pairs (-rating, foodName).
+
+Store ratings as negative in the TreeSet, so the highest-rated food is always the first element.
+
+On changeRating(food, newRating):
+- Remove the old pair (-oldRating, food).
+- Insert the new pair (-newRating, food).
+
+On highestRated(cuisine):
+- Return the first element from the TreeSet.
+
+Time Complexity:
+- Initialization: O(N log N), where N is the number of foods.
+- changeRating: O(log F), where F is the number of foods in the cuisine.
+- highestRated: O(1).
+
+Space Complexity:
+O(N), where N is the number of foods.
+*/
+
+import javafx.util.Pair;
+import java.util.*;
+
+public class FoodRatings {
+
+    private Map<String, TreeSet<Pair<Integer, String>>> cuisinesRatingFood = new HashMap<>();
+    private Map<String, String> foodCuisines = new HashMap<>();
+    private Map<String, Integer> foodRating = new HashMap<>();
+
+    public FoodRatings(String[] foods, String[] cuisines, int[] ratings) {
+        for (int i = 0; i < foods.length; ++i) {
+            foodCuisines.put(foods[i], cuisines[i]);
+            foodRating.put(foods[i], ratings[i]);
+
+            cuisinesRatingFood.computeIfAbsent(cuisines[i], e -> new TreeSet<>(
+                    (a, b) -> a.getKey().equals(b.getKey()) 
+                        ? a.getValue().compareTo(b.getValue()) 
+                        : Integer.compare(a.getKey(), b.getKey())))
+                    .add(new Pair<>(-ratings[i], foods[i]));
+        }
+    }
+
+    public void changeRating(String food, int newRating) {
+        int oldRating = foodRating.get(food);
+
+        TreeSet<Pair<Integer, String>> cuisineSet = cuisinesRatingFood.get(foodCuisines.get(food));
+        cuisineSet.remove(new Pair<>(-oldRating, food));
+
+        foodRating.put(food, newRating);
+        cuisineSet.add(new Pair<>(-newRating, food));
+    }
+
+    public String highestRated(String cuisine) {
+        return cuisinesRatingFood.get(cuisine).first().getValue();
+    }
+}