LeetCode 1127: User Purchase Platform Solution

Master LeetCode problem 1127 (User Purchase Platform), a hard challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

1127. User Purchase Platform

Hard

Database

Problem Explanation

Explanation:

To solve this problem, we can use a combination of heap and hash map data structures. We will maintain a heap to keep track of the purchases made by each user and a hash map to quickly access the user's purchase history. We will iterate through the given user-purchase data and update the heap and hash map accordingly.

Initialize a hash map to store the purchase history of each user, where the key is the user ID and the value is a priority queue (heap) of purchases made by that user.
Iterate through the given user-purchase data:
- If the user ID does not exist in the hash map, create a new priority queue for the user and insert it into the hash map.
- Push the purchase amount to the priority queue of the corresponding user.
For each query, retrieve the user's purchase history from the hash map, calculate the sum of the top k purchases, and add it to the result list.
Return the result list containing the total purchase amount for each query.

Solution Code

import java.util.*;

class UserPurchasePlatform {
    public int[] userPurchasePlatform(int[][] purchases, int[][] queries) {
        Map<Integer, PriorityQueue<Integer>> userPurchases = new HashMap<>();
        
        for (int[] purchase : purchases) {
            int userId = purchase[0];
            int amount = purchase[1];

            userPurchases.putIfAbsent(userId, new PriorityQueue<>());
            userPurchases.get(userId).add(amount);
        }
        
        int[] result = new int[queries.length];
        for (int i = 0; i < queries.length; i++) {
            int userId = queries[i][0];
            int k = queries[i][1];
            
            if (!userPurchases.containsKey(userId)) {
                result[i] = 0;
            } else {
                int sum = 0;
                PriorityQueue<Integer> purchasesHeap = userPurchases.get(userId);
                for (int j = 0; j < k && !purchasesHeap.isEmpty(); j++) {
                    sum += purchasesHeap.poll();
                }
                result[i] = sum;
            }
        }
        
        return result;
    }
}

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