def load_submission(path):
    """return json object.
    Input file format:
        <query_unique_id1> <uid11>,<uid12>,<uid13>,...
        <query_unique_id2> <uid21>,<uid22>,<uid23>,...
        <query_unique_id3> <uid31>,<uid32>,<uid33>,...
    Return json format:
        {
            <query_unique_id1>: [ uid11, uid12, uid13, ... ]
            <query_unique_id2>: [ uid21, uid22, uid23, ... ]
            <query_unique_id3>: [ uid31, uid32, uid33, ... ]
        }
    """
    json_list = {}
    with open(path) as f:
        for line in f:
            line = line.strip()
            tmp = line.split(' ')
            if len(tmp) > 1:
                q_id = tmp[0].strip()
                c_ids = tmp[1].strip().split(',')
                json_list[q_id] = c_ids
    return json_list
