Я попробовал 2-й и 3-й пункты...не могу решить, пожалуйста, помогите мне

I'm developing Exam Scheduler Web Application in php-mysql. 
first point is done but 2nd and 3rd points i can`t understand (how can write the code) plz help me solve in this last 2 points... 

I follow these steps:

1. Manage courses and enrollment in them Create a page that:

1.1. Takes as input a new course code (e.g. CS101) and enrollment in that course in the form of a text file (e.g. CS101.txt). The text file contains a list of students enrolled in that course. For example:
CS101.txt

BC160300123

BC160300234

BC170100345

BC170100456

………….

 1.2.   Updates enrollment in an existing course by giving as input a new file having list of students enrolled in that course.

 1.3.   Delete a course and the corresponding enrollment in it.

2. Calculate list of “Non-overlapping courses” for each course
In the context of this application, a course A is non-overlapping to a course B if there is no student who is enrolled in both the courses A and B. You are required to determine list of all non-overlapping courses for each course. The output can be of the following form:


Course CS101 CS201 ENG101 CS502

List of Non-overlapping Courses CS301, CS304, CS504, CS403, CS601, CS606 CS301, CS304, CS504 ENG201, CS302, CS401 CS602

….. …….

3. Calculate a possible “correct” schedule with minimum number of days
Given ‘n’ number of slots per day, calculate a possible schedule with minimum number of days. Regarding correctness: A schedule will be correct if all the courses whose exams are scheduled on same day are non-overlapping with each other.

i`m tried 2nd an 3rd points, first point is done but 2nd and 3rd points i can`t understand (how can write the code) plz help in these last 2 points...