Parallel Courses

You are given an integer `n` representing the number of courses labeled from `1` to `n`. You are also given a 2D integer array `relations` where `relations[i] = [prevCourse_i, nextCourse_i]` denotes that course `prevCourse_i` must 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 for the courses you are taking in previous semesters. 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: The figure above represents the given graph. In the first semester, you can take courses 1 and 2. In the second semester, you can take course 3. ``` **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**.