docstr: :type numCourses: int
  :type prerequisites: List[List[int]]
  :rtype: bool
docstr_tok: [":","type","numCourses",":","int",":","type","prerequisites",":","List","[","List","[","int","]","]",":","rtype",":","bool"]
code: def canFinish(self, numCourses, prerequisites):
      """
      :type numCourses: int
      :type prerequisites: List[List[int]]
      :rtype: bool
      """
      from collections import defaultdict, deque
  
      # key: index of node; value: GNode
      graph = defaultdict(GNode)
  
      totalDeps = 0
      for relation in prerequisites:
          nextCourse, prevCourse = relation[0], relation[1]
          graph[prevCourse].outNodes.append(nextCourse)
          graph[nextCourse].inDegrees += 1
          totalDeps += 1
  
      # we start from courses that have no prerequisites.
      # we could use either set, stack or queue to keep track of courses with no dependence.
      nodepCourses = deque()
      for index, node in graph.items():
          if node.inDegrees == 0:
              nodepCourses.append(index)
  
      removedEdges = 0
      while nodepCourses:
          # pop out course without dependency
          course = nodepCourses.pop()
  
          # remove its outgoing edges one by one
          for nextCourse in graph[course].outNodes:
              graph[nextCourse].inDegrees -= 1
              removedEdges += 1
              # while removing edges, we might discover new courses with prerequisites removed, i.e. new courses without prerequisites.
              if graph[nextCourse].inDegrees == 0:
                  nodepCourses.append(nextCourse)
  
      if removedEdges == totalDeps:
          return True
      else:
          # if there are still some edges left, then there exist some cycles
          # Due to the dead-lock (dependencies), we cannot remove the cyclic edges
          return False
  
label_desc: Use image node_id 1 for calling the Solution obj's underlying member method code with example usage: obj.canFinish(numCourses, prerequisites) and returns: True, False