Hole type: subroutine
Adding up the digits of a non-negative integer produces a number:
1234567 -> 1+2+3+4+5+6+7 -> 28
Adding up those digits produces another:
28 -> 2+8 -> 10
Repeating this process until only a single digit is left produces a
checksum known as a digital root:
10 -> 1+0 -> 1
Write a subroutine to compute the digital root of any non-negative
integer argument.
| Code | Length |
|---|---|
| sub hole {$_[0]=eval join'+',split//,$_[0]while$_[0]>9;$_[0]} | 50 |
| sub hole {($_)=@_;s/(\d)(\d)/$1+$2/ge while$_>9;$_} | 40 |
| sub hole {$_=pop;1while s/(\d)(\d)/$1+$2/ge;$_} | 36 |
The easy part is adding the digits. The tricky part is separating the digits, and knowing when to stop. The first solution uses a well-known approach; split the digits, join them with '+', and eval the result.
The second and third solutions also use eval, but in the form of /e, and repeatedly add two digits at a time. The second solution stops when the result is less than or equal to 9. The third solution improves this by using the substitution as the conditional; the substitution will return false when there is only one digit left.