def dist(a, b):
    return sum((i-j)**2 for i, j in zip(a, b))
def __init__(self, root, split="train", transforms=None):
        super().__init__(root=root, transforms=transforms)

        verify_str_arg(split, "split", valid_values=("train", "test"))

        root = Path(root) / "hd1k"
        if split == "train":
            # There are 36 "sequences" and we don't want seq i to overlap with seq i + 1, so we need this for loop
            for seq_idx in range(36):
                flows = sorted(glob(str(root / "hd1k_flow_gt" / "flow_occ" / f"{seq_idx:06d}_*.png")))
                images = sorted(glob(str(root / "hd1k_input" / "image_2" / f"{seq_idx:06d}_*.png")))
                for i in range(len(flows) - 1):
                    self._flow_list += [flows[i]]
                    self._image_list += [[images[i], images[i + 1]]]
        else:
            images1 = sorted(glob(str(root / "hd1k_challenge" / "image_2" / "*10.png")))
            images2 = sorted(glob(str(root / "hd1k_challenge" / "image_2" / "*11.png")))
            for image1, image2 in zip(images1, images2):
                self._image_list += [[image1, image2]]

        if not self._image_list:
            raise FileNotFoundError(
                "Could not find the HD1K images. Please make sure the directory structure is correct."
            )