Contents

Description

In this task you will be given several numbers and asked to calculate their sums of digits.

Important: while many programming languages have built-in functions to convert numbers to strings (from which digits could be extracted), you should not use this (since your goal is to learn some programming tricks).

Instead you need to implement algorithm with repetitive division by 10 (base of numeral system) and summing up the remainders.

My solution

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import sys


def sum_digits(x: int) -> int:
    """Sum the digits in `x`.

    Args:
        x: an integer >= 0

    Returns:
        An integer representing the sum of the digits in `x`.

    Examples:
        >>> sum_digits(123)
        6

    """
    result = 0
    quot, rem = divmod(x, 10)
    while quot:
        result += rem
        quot, rem = divmod(quot, 10)
    return result + rem


if __name__ == "__main__" and len(sys.argv) > 1:
    with open(sys.argv[1], "r") as f:
        lines = f.readlines()
        testcases = ((int(x) for x in line.split(" ")) for line in lines[1:])

        def abc(a, b, c):
            """Massage input to requirements of problem."""
            return a * b + c

        for xs in testcases:
            n = abc(*xs)
            print(sum_digits(n))

Tests

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from solution import sum_digits
from hypothesis import given
from hypothesis.strategies import integers


def test_sum_digits_mytest_simple():
    """My initial tests."""
    assert sum_digits(0) == 0, "expected sum 0 for value 0"
    assert sum_digits(1) == 1, "expected sum 1 for value 1"
    assert sum_digits(10) == 1, "expected sum 1 for value 10"
    assert sum_digits(123) == 6, "expected sum 6 for value 123"


def test_sum_digits_mytest_range():
    """My initial test for a range of integers."""
    numstr, total = "1", 1
    for i in range(2, 10):
        numstr += str(i)
        total += i
        assert (
            sum_digits(int(numstr)) == total
        ), f"expected sum {total} for value {numstr}"


def test_provided():
    """Tests provided with problem."""
    assert sum_digits(1492) == 16, "expected sum 16 for value 1492"
    assert sum_digits(1776) == 21, "expected sum 21 for value 1776"
    assert (
        sum_digits(11 * 9 + 1) == 1
    ), f"expected sum 1 for value \
            {11*9+1}"
    assert (
        sum_digits(14 * 90 + 232) == 16
    ), f"expected sum 16 for value \
            {14*90+232}"
    assert (
        sum_digits(111 * 15 + 111) == 21
    ), f"expected sum 21 for value \
            {111*15+111}"


def gen_int():
    """Configure generation for test_property_test()."""
    return integers(min_value=0, max_value=100)


@given(gen_int(), gen_int(), gen_int())
def test_property_test(a, b, c):
    """Property test using a range of integers."""
    n = a * b + c
    _sum = sum(int(x) for x in tuple(str(n)))
    assert sum_digits(n) == _sum, f"expected sum {_sum} for value n"