def convert_cnt_digit(int_list):
    """
    given a list of integers, i.e. [10, 213], convert each element in the list into
    [number of digits, digit 1...] structure. example list will be converted into [2,1,0,3,2,1,3]
    which [2,1,0] represents 10 and [3,2,1,3] represents 213
    :param int_list: list of integers
    :return: digit list
    """
    digit_list = []
    for num in int_list:
        num = str(num)
        num_len = len(num)
        digit_list.append(num_len)
        for i in range(num_len):
            digit_list.append(int(num[i]))
    return digit_list
