# There are a total of n courses you have to take labelled from 0 to n - 1.

# Some courses may have prerequisites, for example, if prerequisites[i] = [ai, bi] this means you must take the course bi before the course ai.

# Given the total number of courses numCourses and a list of the prerequisite pairs, return the ordering of courses you should take to finish all courses.

# If there are many valid answers, return any of them. If it is impossible to finish all courses, return an empty array.


# Example 1:

# Input: numCourses = 2, prerequisites = [[1,0]]
# Output: [0,1]
# Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So the correct course order is [0,1].
# Example 2:

# Input: numCourses = 4, prerequisites = [[1,0],[2,0],[3,1],[3,2]]
# Output: [0,2,1,3]
# Explanation: There are a total of 4 courses to take. To take course 3 you should have finished both courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0.
# So one correct course order is [0,1,2,3]. Another correct ordering is [0,2,1,3].
# Example 3:

# Input: numCourses = 1, prerequisites = []
# Output: [0]
