LeetCode 1107: New Users Daily Count Solution

Master LeetCode problem 1107 (New Users Daily Count), a medium 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.

1107. New Users Daily Count

Medium

Database

Problem Explanation

Explanation

To solve this problem, we can iterate through the given list of events and maintain a count of the number of new users each day. We can use a HashMap to store the count of new users for each day. We will then iterate through the HashMap to calculate the total number of new users for each day.

Algorithm:

Initialize a HashMap to store the count of new users for each day.
Iterate through the list of events:
- If the event is "signup", increment the count of new users for that day in the HashMap.
- If the event is "follow", increment the count of new users for the next day in the HashMap.
Iterate through the HashMap to calculate the total number of new users for each day.

Time complexity: O(n), where n is the number of events in the input list. Space complexity: O(n), where n is the number of days in the input list.

Solution Code

import java.util.*;

class Solution {
    public int[] dailyUserCount(int[][] events) {
        Map<Integer, Integer> userCount = new HashMap<>();
        
        for (int[] event : events) {
            if (event[1] == 1) {
                userCount.put(event[0], userCount.getOrDefault(event[0], 0) + 1);
            } else {
                userCount.put(event[0] + 1, userCount.getOrDefault(event[0] + 1, 0) + 1);
            }
        }
        
        int maxDay = userCount.keySet().stream().max(Integer::compare).orElse(0);
        int[] result = new int[maxDay + 1];
        
        for (int day : userCount.keySet()) {
            result[day] = userCount.get(day);
        }
        
        return result;
    }
}

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