canFinish(1, [[1,0]]) // true - to take course 1 you should have finished course 0
canFinish(2, [[1,0],[0,1]]) // false - to take course 1 you have to have finished course 0, to take 0 you have to have finished course 1
canFinish(1, []) // true
canFinish(3, [[1,0],[2,0]]) // true
canFinish(3, [[2,0],[2,1]] ) // true
canFinish(10, [[5,6],[0,2],[1,7],[5,9],[1,8],[3,4],[0,6],[0,7],[0,3],[8,9]]) // true