Parallel Courses⚓︎
Description⚓︎
You are given an integer n
, which indicates that there are n
courses labeled from 1
to n
. You are also given an array relations where relations[i] = [prevCourse_i, nextCourse_i]
, representing a prerequisite relationship between course prevCoursei
and course nextCourse_i
: course prevCourse_i
has to be taken before course nextCourse_i
.
In one semester, you can take any number of courses as long as you have taken all the prerequisites in the previous semester for the courses you are taking.
Return the minimum number of semesters needed to take all courses. If there is no way to take all the courses, return -1
.
Example 1:
- Input:
n = 3, relations = [[1,3],[2,3]]
- Output:
2
- Explanation:
Example 2:
- Input:
n = 3, relations = [[1,2],[2,3],[3,1]]
- Output:
-1
- Explanation: No course can be studied because they are prerequisites of each other.
Constraints:
1 <= n <= 5000
1 <= relations.length <= 5000
relations[i].length == 2
1 <= prevCourse_i, nextCourse_i <= n
prevCourse_i != nextCourse_i
- All the pairs
[prevCourse_i, nextCourse_i]
are unique.