def map_class_names(src_classes, dst_classes):
    """Computes src to dst index mapping

    src2dst[src_idx] = dst_idx
    #  according to class name matching, -1 for non-matched ones
    assert(len(src2dst) == len(src_classes))
    ex)
      src_classes = ['person', 'car', 'tree']
      dst_classes = ['tree', 'person', 'sky', 'ball']
      -> Returns src2dst = [1, -1, 0]
    """
    src2dst = []
    for src_class in src_classes:
        if src_class in dst_classes:
            src2dst.append(dst_classes.index(src_class))
        else:
            src2dst.append(-1)
    return src2dst