code: def swap_vertices(self, i, j):
          
          store_vertex_i = self.vertices[i]
          store_vertex_j = self.vertices[j]
          self.vertices[j] = store_vertex_i
          self.vertices[i] = store_vertex_j
          for k in range(len(self.vertices)):
              for swap_list in [self.vertices[k].children, self.vertices[k].parents]:
                  if i in swap_list:
                      swap_list[swap_list.index(i)] = -1
                  if j in swap_list:
                      swap_list[swap_list.index(j)] = i
                  if -1 in swap_list:
                      swap_list[swap_list.index(-1)] = j
docs: Swap two vertices in the tree structure array.
          swap_vertex swaps the location of two vertices in a tree structure array. 
  
          :param tree: the tree for which two vertices are to be swapped.
          :param i: the index of the first vertex to be swapped.
          :param j: the index of the second vertex to be swapped.
          :rval tree: the tree structure with the two vertex locations swapped.