course_schedule.py

def canFinish(numCourses, prerequisites):
  """
  :type numCourses: int
  :type prerequisites: List[List[int]]
  :rtype: bool
  """
  if prerequisites:
    # create graph
    courses = {}
    finished_courses = []
    for i in range(numCourses):
      courses[i] = set()
    # put prereqs
    for prereq in prerequisites:
      courses[prereq[0]].add(prereq[1])
    # find classes without prereqs and add to queue to complete first
    queue = []
    for course in courses:
      # pass if empty set
      if not courses[course]:
        queue.append(course)
    while queue:
      course = queue.pop()
      for c, r in courses.items():
        if course in r:
          r.remove(course)
            if not r:
              queue.append(c)
      finished_courses.append(course)
    return len(finished_courses) == numCourses
  return True