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Count User Logins 🌿 (Singapore)

🤘 INTERN

A company wants to track the usage of its mobile app by recording users' login times and dates. The company stores the login information in a 2D array of strings, logs, which contains data in the format ["/username<user_id>","login_time","login_date"].

They need a function to process the logs and output a 2D array of strings, sorted lexicographically, that displays the number of times each user logs in per day in the format ["/username<user_id>","login_date","login_count"]. It must filter invalid data in the input array rather than write it to the output array.

Users should be sorted in lexicographic order based on their user_id. Each user's information should be sorted by the login date in ascending order. The date and time are provided in YYYY-MM-DD and HH:MM:SS format, and the username has the format "userX" where X is an integer.

Function Description

Complete the function countUserLogins in the editor.

countUserLogins has the following parameter:

String[][] logs: a 2D array of strings containing the login data

Returns

String[][]: a 2D array of strings containing the user login counts per day, sorted lexicographically

Example 1:

Input:  logs = [["user1","09:00:00","2021-01-01"],["user1","13:00:00","2021-01-01"],["user2","14:00:00","2021-01-01"],["user1","20:00:00","2021-01-02"],["user2","21:00:00","2021-01-01"]]
Output: [["user1","2021-01-01","2"],["user1","2021-01-02","1"],["user2","2021-01-01","2"]] 
Explanation:


The function should output the login counts for each user per day, sorted lexicographically, resulting in a 2-d array of strings in the format [["user1","2021-01-01","3"],["user1","2021-01-02","1"],["user2","2021-01-01","1"]].

Example 2:

Input:  logs = [["user1","09:00:00","2021-01-01"],["user1","13:00:00","2021-01-01"],["user2","14:00:00","2021-01-01"],["user1","20:00:00","2021-01-01"],["user2","21:00:00","2021-01-01"], ["user3","25:00:00","2021-01-01"], ["user4","22:00:00","2021-02-29"]]
Output: [["user1","2021-01-01","3"],["user2","2021-01-01","2"]] 
Explanation:
user1 logs into the system 3 times on 2021-01-01

user2 logs into the system 3 times on 2021-01-01

entry 6 in the logs has an invalid time, 25:00:00.

entry 7 in the logs has an invalid data, 2021-02-29.

Constraints:

1 ≤ n (size of logs) ≤ 10^5

2000 ≤ YYYY ≤ 3000

0 ≤ MM, DD, HH, SS ≤ 99

YYYY, MM, DD, HH, and SS are all integers.

All usernames are of the format "user" appended with some integer (user_id).