Course Schedule

The problem There are a total of numCourses courses you have to take, labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai, bi] indicates that you must take course bi first if you want to take course ai. For example, the pair [0, 1] indicates that to take course 0, you have to first take course 1. Return true if you can finish all courses. Otherwise, return false. ...