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I’ve been doing the Weekly Challenges. The latest involved extracting digital roots. (Note that this ends today.)

Task 1: Digital Root

You are given a positive integer, $int.

Write a function that calculates the additive persistence of a positive integer and also return the digital root.

Digital root is the recursive sum of all digits in a number until a single digit is obtained.

Additive persistence is the number of times you need to sum the digits to reach a single digit.

As usual I avoided string conversions. This Raku code is the same algorithm I used in all the other languages.

sub digitalroot($a) {

Initialise count ahd rolling value.

    my $count = 0;
    my $value = $a;

If the value is more than one digit:

    while ($value > 9) {

Initialise a new value.

        my $p = 0;

While there are digits left,

        while ($value > 0) {

Add the last digit to the new value,

            $p += $value % 10;

And shift the rest of them to the right.

            $value = floor($value / 10);
        }

Copy that into the rolling value, and increment the count. Then loop back and check again.

        $value = $p;
        $count++;
    }

Return the results.

    [$count, $value];
}

Task 2 is a duplicate of Challenge 340 task 1, and I haven't added any new languages since then.

Full code on github.