There are numCourses courses labeled 0 to numCourses - 1. prerequisites[i] = [a, b] means you must take course b before course a. Return true if you can finish every course, i.e. the prerequisites don't form a cycle.
Example
Input: numCourses = 2, prerequisites = [[1, 0]]
Output: true // take 0, then 1
Input: numCourses = 2, prerequisites = [[1, 0], [0, 1]]
Output: false // 0 needs 1 and 1 needs 0