from typing import List


def reformat_span_idxs(span_idx_list: List[List[int]]) -> list:
    """
    Reformat span idxs to look like [0, [start_idx, end_idx]]
    """
    span_idxs = [x[0] for x in span_idx_list]

    start_idx = min(span_idxs)
    end_idx = max(span_idxs)
    return [0, [start_idx, end_idx]]