def _broadcast_timestamps(csc, dst_timestamps):
    """Broadcast the timestamp of each destination node to its corresponding
    source nodes."""
    return expand_indptr(
        csc.indptr, node_ids=dst_timestamps, output_size=len(csc.indices)
    )
Broadcast the timestamp of each destination node to its corresponding
    source nodes.
python/dgl/graphbolt/internal/sample_utils.py