code: def label_correcting_check_cycle(self, j, pred):
          '''
          API:
              label_correcting_check_cycle(self, j, pred)
          Description:
              Checks if predecessor dictionary has a cycle, j represents the node
              that predecessor is recently updated.
          Pre:
              (1) predecessor of source node should be None.
          Input:
              j: node that predecessor is recently updated.
              pred: predecessor dictionary
          Return:
              If there exists a cycle, returns the list that represents the
              cycle, otherwise it returns to None.
          '''
          labelled = {}
          for n in self.neighbors:
              labelled[n] = None
          current = j
          while current != None:
              if labelled[current]==j:
                  cycle = self.label_correcting_get_cycle(j, pred)
                  return cycle
              labelled[current] = j
              current = pred[current]
          return Nonf label_correcting_check_cycle(self, j, pred):
          '''
          API:
              label_correcting_check_cycle(self, j, pred)
          Description:
              Checks if predecessor dictionary has a cycle, j represents the node
              that predecessor is recently updated.
          Pre:
              (1) predecessor of source node should be None.
          Input:
              j: node that predecessor is recently updated.
              pred: predecessor dictionary
          Return:
              If there exists a cycle, returns the list that represents the
              cycle, otherwise it returns to None.
          '''
          labelled = {}
          for n in self.neighbors:
              labelled[n] = None
          current = j
          while current != None:
              if labelled[current]==j:
                  cycle = self.label_correcting_get_cycle(j, pred)
                  return cycle
              labelled[current] = j
              current = pred[current]
          return None
docs: API:
              label_correcting_check_cycle(self, j, pred)
          Description:
              Checks if predecessor dictionary has a cycle, j represents the node
              that predecessor is recently updated.
          Pre:
              (1) predecessor of source node should be None.
          Input:
              j: node that predecessor is recently updated.
              pred: predecessor dictionary
          Return:
              If there exists a cycle, returns the list that represents the
              cycle, otherwise it returns to None.