Problem D
Course Scheduling
It is a difficult job to schedule all of the courses in a university to satisfy students’ choices with a minimum of conflicts. The task is made all the more difficult when some students don’t pre-enroll, or pre-enroll multiple times because they forget that they already did it.
Input
The first line of input contains an integer $0 \le n \le 100\, 000$, the number of student course requests. Each of the next $n$ lines contains three strings separated by spaces: a student’s first and last name, and the course that the student wishes to take. You may assume that each name is a string of at least one and at most $20$ upper-case letters, and that a course is a string of at least one and at most $10$ upper-case letters and digits. If a student requests a given course more than once, only the first such request should be considered. You may assume that no two students have both their first and last names the same.
Output
For each requested course, output a line containing the course, a space, and the number of students who requested the course. Output the courses sorted in lexicographical order (with digits sorted before letters).
| Sample Input 1 | Sample Output 1 |
|---|---|
4 PINK TIE CS241 JOHN DOE CS241 JOHN DOE CSS JOHN DOE CSS |
CS241 2 CSS 1 |
