def search(bs, arr):
    """
    Binary search recursive function.
    :param bs: int
        What to search
    :param arr: array
        Array of ints where to search. Array must be sorted.
    :return: string
        Position of required element or "cannot found" string
    """

    length = len(arr)
    check_item = arr[int(length / 2)]

    if check_item == bs:
        return str(check_item) + ' is on position ' + str(arr[int(length / 2)])

    if check_item < bs:
        return search(bs, arr[int(length / 2):])

    if check_item > bs:
        return search(bs, arr[:int(length / 2)])

    return "cannot found"


# Test dataset.
data = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29,
        30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57,
        58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85,
        86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110,
        111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132,
        133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148]

print(search(19, data))
