comefrom: <qiyuangong>126_Word_Ladder_II_1.py
code: def add_path(tree, word, neigh, is_forw):
      if is_forw:
          tree[word] = tree.get(word, []) + [neigh]
      else:
          tree[neigh] = tree.get(neigh, []) + [word]
masked: def sample_funcname ( var_0 , var_1 , var_2 , var_3 ) :
      if var_3 :
          var_0 [ var_1 ] = var_0.get ( var_1 , [ ] ) + [ var_2 ]
      else :
          var_0 [ var_2 ] = var_0.get ( var_2 , [ ] ) + [ var_1 ]
  