Email Log Processing / Grouping and Sorting

Problem: Email Log Processing (Grouping + Rule-based Sorting) You are given a list of email event logs logs. Each log is a single line string in the format: <timestamp> <sender_email> <receiver_email> <subject> timestamp: a non-negative integer (seconds since epoch) sender_email, receiver_email: strings without spaces subject: the remainder of the line starting from the 4th token; it may contain spaces (and may be empty) Your task is to group logs by sender_email, sort each group by specific rules, and print the result. Rules Group by sender_email. Within the same sender_email, sort logs by: timestamp ascending if equal, receiver_email lexicographically ascending if still equal, subject lexicographically ascending Output sender groups in lexicographical order of sender_email. Input Line 1: integer n, number of logs. Next n lines: one log per line. Output For each sender, print: sender: <sender_email> Then print each sorted log line as: <timestamp> <receiver_email> <subject> Note: sender_email is not printed on the log lines. Constraints 1 <= n <= 2 * 10^5 0 <= timestamp <= 10^9 Each line length <= 300 Example Input 5 100 alice@a.com bob@b.com hello 90 alice@a.com carl@c.com meeting notes 90 dan@d.com e@e.com hi 90 alice@a.com bob@b.com a-subject 100 dan@d.com a@a.com ping Output sender: alice@a.com 90 bob@b.com a-subject 90 carl@c.com meeting notes 100 bob@b.com hello sender: dan@d.com 90 e@e.com hi 100 a@a.com ping Example Input 1 0 a@a.com b@b.com hi Output sender: a@a.com 0 b@b.com hi