Course Schedule

There are `numCourses` courses labelled 0..numCourses-1. Each `prerequisites[i] = [a, b]` means b must be taken before a. Return true if you can finish every course (i.e. there is no cyclic dependency). Example: (2, [[1, 0]]) → true; (2, [[1, 0], [0, 1]]) → false.