Example 1:
Input: n = 4, relations = [[2,1],[3,1],[1,4]], k = 2
Output: 3
Explanation:
Example 2:
Input: n = 5, relations = [[2,1],[3,1],[4,1],[1,5]], k = 2
Output: 4
Explanation:
Example 3:
Input: n = 11, relations = [], k = 2
Output: 6
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] = [prevCoursei, nextCoursei], representing a prerequisite relationship between course prevCoursei and course nextCoursei: course prevCoursei has to be taken before course nextCoursei.
In one semester, you can take at most k courses as long as you have completed all prerequisites for the courses in previous semesters.
Return the minimum number of semesters needed to take all courses.
Take courses 2 and 3 in semester 1, course 1 in semester 2, and course 4 in semester 3.
At most two courses can be taken per semester, so course 1 is delayed by prerequisites.
1 <= n <= 151 <= k <= n0 <= relations.length <= n * (n - 1) / 2relations[i].length == 21 <= prevCoursei, nextCoursei <= nprevCoursei != nextCoursei[prevCoursei, nextCoursei] are unique.