Dutch Burgerservicenummer (BSN) eleven-test

Question

Introduction:

A Dutch BSN (BurgerServiceNummer) is valid when it complies to the following rules:

• It only contains digits.
• The length should be either 8 or 9 in length.
• When the digits are indexed as A through I, the result of the following sum: 9xA + 8xB + 7xC + 6xD + 5xE + 4xF + 3xG + 2xH + -1xI (NOTE the -1 instead of 1!) should be divisible by 11, and should not be 0.

Challenge:

Input: A string or char-array representing the BSN.

Output: A truthy or falsey result whether the input is a valid BSN.

Challenge Rules:

• The input format should be a string or char-array. You are not allowed to use an int-array of digits, or a (possibly octal) number. (You are allowed to convert it to an int-array of digits yourself, though, but not directly as argument.)
• Despite the restriction on the input above, you can assume all test cases will contain one or more digits ([0-9]+)
• Regarding the BSN with length 8 instead of 9, the Dutch Wikipedia states the following: "For the eleven-test and for other practical uses, a leading zero is added to make the number of length 9." (source)

General rules:

• This is code-golf, so shortest answer in bytes wins.
  Don't let code-golf languages discourage you from posting answers with non-codegolfing languages. Try to come up with an as short as possible answer for 'any' programming language.
• Standard rules apply for your answer, so you are allowed to use STDIN/STDOUT, functions/method with the proper parameters, full programs. Your call.
• Default Loopholes are forbidden.
• If possible, please add a link with a test for your code.
• Also, please add an explanation if necessary.

Test cases:

// Truthy test cases:
111222333
123456782
232262536
010464554
10464554
44016773

// Falsey test cases:
000000000
192837465
247594057
88888888
73
3112223342
000000012

Answer 1

JavaScript (ES6) 57

Input as an array of chars. reduceRight saves the day!

s=>!(i=1,t=s.reduceRight((t,v)=>t-v*++i),!t|t%11|(i|1)-9)

Test

F=
s=>!(i=1,t=s.reduceRight((t,v)=>t-v*++i),!t|t%11|(i|1)-9)


;['111222333','123456782','232262536','010464554','10464554','44016773']
.forEach(t=>{
  var r=F([...t]);console.log(t,r)
})

;['000000000','192837465','247594057','88888888','73','3112223342','3112223342']
.forEach(t=>{
  var r=F([...t]);console.log(t,r)
})

Answer 2

05AB1E, 23 21 bytes

`()DgLR*OD11Ö89¹gåP0Ê

Try it online! or as a Test suite

Explanation

`                        # push input as individual chars onto stack
 (                       # negate top value
  )                      # wrap in list
   DgLR                  # range [len(input) ... 1]
       *O                # multiply with list of digits and sum
         D11Ö            # is evenly divisible by 11
             89¹gå       # len(input) is 8 or 9
                  P      # product of sum/divisible by 11/len in (8,9)
                   0Ê    # not equal to 0

Answer 3

R, 86 67 bytes

Edit: Thanks to Jarko Dubbeldam for suggesting the dot product!

l=length(x<-scan(,""));s=as.double(x)%*%c(l:2,-1);!s%%11&s&l>7&l<10

Reads input from stdin and store as an array/vector of characters. Subsequently convert to numeric,multiply with the vector 9...2,-1 and check all conditions.

Answer 4

JavaScript (ES6), 61 60 59 58 bytes

Takes an array of chars as input. Returns false / true.

a=>!(a.map(c=>s-=--k?-c*k-c:c,k=a.length&9,s=0)|!s|k|s%11)

Test cases

let f =

a=>!(a.map(c=>s-=--k?-c*k-c:c,k=a.length&9,s=0)|!s|k|s%11)

// truthy
console.log(f([..."111222333"]));
console.log(f([..."123456782"]));
console.log(f([..."232262536"]));
console.log(f([..."010464554"]));
console.log(f([..."10464554"]));
console.log(f([..."44016773"]));

// falsy
console.log(f([..."000000000"]));
console.log(f([..."192837465"]));
console.log(f([..."247594057"]));
console.log(f([..."88888888"]));
console.log(f([..."73"]));
console.log(f([..."3112223342"]));

Answer 5

C, 112 101 96 98 104 bytes

Thanks to @MartinEnder for saving 5 3 bytes while fixing my code!

j,i,k,l;f(char*s){l=strlen(s);for(i=l,j=k=0;j<l;)k+=(s[j++]-48)*(i>1?i--:-1);return!(k%11)&&k&&(l^8)<2;}

Returns 0 if invalid, 1 if valid. Try it online!

Answer 6

R, 95 79 93 bytes

function(x){y=as.double(el(strsplit(x,"")));z=y%*%c((q<-length(y)):2,-1);(z&!z%%11&q>7&q<10)}

Unnamed function that takes a string as argument. At first I overread the requirement of having a string as input instead of a number, but that's good, because it saves some bytes on conversion.

I am not sure how to interpret the array of characters, but if that means that you can use a vector of stringed digits "1" "2" "3" "4" etc as input, it becomes a bit shorter even:

function(x){y=as.double(x);z=y%*%c((q<-length(y)):2,-1);(z&!z%%11&q>7&q<10)}

Splits x into a numeric vector, then appends a 0 if length is 8, then calculates the dotproduct of vector y and c(9,8,7,6,5,4,3,2,-1). Tests if the result is both nonzero and divisible by 11.

Saved 16 bytes thanks to the logic by @Emigna, implicitly appending the 0 in the creation of the vector c(length(x):2,-1).

Forgot to add check for length 8/9, so +14 bytes :(

Answer 7

Perl, 58 bytes (52 + 6)

@N=(-1,2..9);$r+=$_*shift@N for reverse@F;$_=$r&&/^\d{8,9}$/&&!($r%11)

Run with

perl -F// -lapE

Input passed through STDIN:

Usage

echo 232262536 | perl -F// -lapE '@N=(-1,2..9);$r+=$_*shift@N for reverse@F;$_=$r&&/^\d{8,9}$/&&!($r%11)'

---

Outputs 1 for as the truthy value, 0 or nothing for falsey values.

Answer 8

C++14, 107 106 bytes

-1 byte for int instead of auto in for loop.

As unnamed lambda returning via reference parameter. Requires input to be std::string or a container of char, like vector<char>.

[](auto c,int&r){int i=c.size();r=7<i&&i<10?-2*c.back()+96:~1<<9;for(int x:c)r+=(x-48)*i--;r=r%11<1&&r>0;}

Ungolfed and usage:

#include<iostream>
#include<string>

auto f=
[](auto c, int& r){
 int i = c.size();
 //if the size is correct, init r to -2*I so we can add I safely later
 //otherwise such a big negative number, that the final test fails
 r = 7<i && i<10 ? -2*c.back()+96 : ~1<<9;
 for (auto x:c)
  r += (x-48)*i--;
 r = r%11<1 && r>0;
}
;

using namespace std;
using namespace std::literals;

int main(){
 int r;
 f("111222333"s,r); std::cout << r << std::endl;
 f("123456782"s,r); std::cout << r << std::endl;
 f("010464554"s,r); std::cout << r << std::endl;
 f("10464554"s,r); std::cout << r << std::endl;
 f("44016773"s,r); std::cout << r << std::endl;
 std::cout << std::endl;
 f("000000000"s,r); std::cout << r << std::endl;
 f("192837465"s,r); std::cout << r << std::endl;
 f("73"s,r); std::cout << r << std::endl;
 f("88888888"s,r); std::cout << r << std::endl;
 f("3112222342"s,r); std::cout << r << std::endl;
 std::cout << std::endl;
 f("99999999"s,r); std::cout << r << std::endl;
 f("999999999"s,r); std::cout << r << std::endl;
}

Answer 9

Jelly, 21 bytes

V€U×JN1¦µL:2=4×Sµ11ḍa

TryItOnline! or run all test cases

Truthy return values are non-zero (and are, in fact, the multiple of 11 sum).

How?

V€U×JN1¦µL:2=4×Sµ11ḍa - Main link: string of digits  e.g. "111222333"
V€                    - eval each - effectively cast each to an integer (keeps leading zeros)
  U                   - upend                        e.g. [ 3, 3, 3, 2, 2, 2, 1, 1, 1]
    J                 - range(length)                e.g. [ 1, 2, 3, 4, 5, 6, 7, 8, 9]
   ×                  - multiply                     e.g. [ 3, 6, 9, 8,10,12, 7, 8, 9]
      1¦              - apply to index 1 (first element)
     N                -     negate                   e.g. [-3, 6, 9, 8,10,12, 7, 8, 9]
        µ             - monadic chain separation   e.g. z=[-3, 6, 9, 8,10,12, 7, 8, 9]
         L            - length(z)                    e.g. 9
          :2          - integer divide by 2          e.g. 4
            =4        - equals 4?                    e.g. 1
               S      - sum(z)                       e.g. 66
              ×       - multiply                     e.g. 66
                µ     - monadic chain separation   e.g. z=66
                 11ḍ  - divides(11, z)               e.g. 1
                    a - and z (for z=0 case)         e.g. 66 (truthy)

Answer 10

Befunge, 72 bytes

>+~>:0`v
^1\-*68_\2/4-!00p*8>1-10p\910gv
@.!+!\%+56:*g00$  _^#!:g01+*-<<

Try it online!

Explanation

>+~>:0`v            Read characters from stdin until EOF, converting each digit into
^1\-*68_              a number on the stack, and keeping a count of the characters read.

      \2/4-!00p     Save !(count/2-4), which is only true for valid lengths (8 and 9).
               *    Multiply the EOF (-1) with the final digit; this is the initial total.

8>1-10p\910gv       Loop over the remaining 8 digits, multiplying each of them by 9-i and
 ^#!:g01+*-<<         add to the total; i goes from 7 down to 0, so 9-i goes from 2 to 9.

               $    Drop the loop counter.
           *g00     Multiply total by the length calculation (invalid lengths become 0).
      %+65:         Make a copy of the total, and calculate modulo 11.
    !\              Boolean not the other copy to check for zero. 
  !+                !(total%11 + !(total)) is only true for non-zero multiples of 11.
@.                  Output the result and exit.

Answer 11

MATL, 36 bytes

Not the longest MATL program I've ever written, but I like how if/else statements get very lengthy very quickly in golfing languages. I feel that this solution may not be optimal in MATL, but as of yet I can't optimize it any further. I'm thinking of using the double 0 somewhere, and maybe cut down on the t's everywhere.

48-tn8=?0wh]tn9=?P[a2:9]*st11\~Y&}x0

Try it online! Explanation:

48-                                  % Subtract 48 (ASCII '0')
   tn                                % Duplicate. Get length.
     8=?                             % If length equals 8
        0wh                          %     Prepend 0 to the duplicate
           ]                         % End if.
            t                        % Duplicate again.
             n9=?                    % If length equals 9.
                 P                   %     Reverse the duplicate
                  [a2:9]*            %     Element-wise product with [-1 2 ... 9]
                         s           %     Sum
                          t11\       %     Duplicate sum, modulus 11
                              ~Y&    %     Result on stack: modulus==0 AND sum!=0
                                 }   % Else
                                  x0 %     Remove the duplicate. Put 0 on stack.
                                     % Display implicitly.

Answer 12

PowerShell v2+, 96 bytes

param($n)$i=8-($n.count-eq8);!(($b=($n|%{(-"$_",(($i+1)*+"$_"))[!!$i--]})-join'+'|iex)%11)-and$b

OK, I'll admit, this looks like a complete mess. And it kinda is. But, bear with me and we'll get through it.

We take input $n (as a char-array) and set $i equal to 8 minus a Boolean value for whether there are 8 items in $n. Meaning, if there are 8 items, then $i would be 7.

The next section combines the calculation with our output. Working from the inside, we loop through $n with $n|%{...}. Each iteration, we use a pseudo-ternary to come up with one of two results -- either -"$_" or (($i+1)*+"$_"). The index is based on whether $i is 0 or not (i.e., we've hit the -1xI case from the challenge equation), which gets post-decremented for the next go-round. Those are all gathered up in parens and -joined together with +. For example, with input 111222333 at this point we'd have 9+8+7+12+10+8+9+6+-3. That is piped to iex (short for Invoke-Expression and similar to eval) before being stored into $b. We then take that %11 and perform a Boolean-not !(...) on that (i.e., so if it is divisible by 11, this portion is $true). That's coupled with -and$b to ensure that $b is non-zero. That Boolean result is left on the pipeline and output is implicit.

Examples

PS C:\Tools\Scripts\golfing> 111222333,123456782,232262536,010464554,10464554,44016773|%{"$_ -> "+(.\dutch-burgerservicenummer.ps1 ([char[]]"$_"))}
111222333 -> True
123456782 -> True
232262536 -> True
10464554 -> True
10464554 -> True
44016773 -> True

PS C:\Tools\Scripts\golfing> 000000000,192837465,247594057,88888888,73,3112223342,000000012|%{"$_ -> "+(.\dutch-burgerservicenummer.ps1 ([char[]]"$_"))}
0 -> False
192837465 -> False
247594057 -> False
88888888 -> False
73 -> False
3112223342 -> False
12 -> False

Answer 13

MATL, 26 bytes

!UGg*R!s0&)s-t11\~Gn8-tg=v

The result is a non-empty column vector, which is truthy iff all its entries are nonzero.

Try it online!

Or verify all test cases with each result on a different line.

Explanation

This tests the three conditions in the following order:

1. Weighted sum is nonzero;
2. Weighted sum is dividible by 11;
3. Length is 8 or 9.

Consider input '8925' for the explanation. ; is the row separator for matrices.

!     % Implicit input. Transpose into a column vecvtor
      % STACK: ['8'; '9'; '2'; '5']
U     % Convert each digit to number
      % STACK: [8; 9; 2; 5]
Gg    % Push a row array of ones as long as the input
      % STACK: [8; 9; 2; 5], [1 1 1 1]
*     % Multiply, element-wise with broadcast
      % STACK: [8 8 8 8; 9 9 9 9; 2 2 2 2; 5 5 5 5]
R     % Upper triangular part
      % STACK: [8 8 8 8; 0 9 9 9; 0 0 2 2; 0 0 0 5]
!     % Transpose
      % STACK: [8 0 0 0;8 9 0 0;8 9 2 0;8 9 2 5]
s     % Sum of each column. This multiplies last element by 1, second-last by 2 etc
      % STACK: [32 27 4 5]
0&)   % Split into last element and remaining elements
      % STACK: 5, [32 27 4]
s     % Sum of array
      % STACK: 5, 63
-     % Subtract
      % STACK: -58. This is the result of condition 1
t11\  % Duplicate. Modulo 11
      % STACK: -58, 8
~     % Logical negation
      % STACK: -58, 0. This gives condition 2
Gn    % Push numnber of entries in the input
      % STACK: -58, 0, 4
8-    % Subtract 8. For valid lengths (8 or 9) this gives 0 or 1
      % STACK: -58, 0, -4
tg    % Duplicate. Convert to logical: set nonzero values to 1
      % STACK: -58, 0, -4, 1
=     % 1 if equal, 0 otherwise. Lenghts 8 or 9 will give 1. This is condition 3
      % STACK: -58, 0, 0
v     % Vertically concatenate the entire stack. This is truthy iff all values 
      % are non-zero. Implicitly display
      % STACK: [-58; 0; 0]

Answer 14

Haskell, 116 112 102 bytes

f x=div(length x)2==4&&g x>0&&h x
h=((==0).(`mod`11)).g
g=sum.zipWith(*)(-1:[2..]).map(read.(:[])).reverse

g counts the sum used in the eleven-proef of h, while f also checks for the correct length and that the eleven-proef is not 0. Especially the checks of f take a lot of bytes.

EDIT: saved 10 bytes thanks to Lynn and div rounding down.

Answer 15

PHP 139 128 bytes

 $u=-1;$i=$argv[1];while($u<=strlen($i)){$c+=($u*(substr($i,-(abs($u)),1)));$u +=$u<0?3:1;}echo($c>0&&!($c%11)&&$u>8&&$u<11?1:0);

Could not get the CLI to just echo the true of false. Had to make do it this way. Any ideas?

128 bytes: Turned "true" and "false" to 1 and 0.

Answer 16

Python 3.8 (pre-release), 111 110 104 bytes

-1 byte thanks to @Kevin-cruijssen

-6 bytes by reading the rules (yay)

lambda s:len(s)in(8,9)and not(x:=sum(a:=[*map(lambda n,m:int(n)*m,s[::-1],range(1,10))])-2*a[0])%11and x

Try it online!

There's probably more golfing to do, but this is what I have for now.

Answer 17

Python 2, 102 bytes

def f(i):S=sum(a*b for a,b in zip([-1]+range(2,10),map(int,i)[::-1]));return(7<len(i)<10)*(S%11<1)*S>0

Answer 18

Python 2, 96 bytes

def g(s):u=7<len(s)<10and sum(x*int(('0'+s)[-x])for x in range(2,10))-int(s[-1]);print(u%11<1)*u

Takes a string as input. The function adds a '0' to the front of the string whether it needs it or not, and uses Python's negative indices to add elements, starting from the end of the string and working back-to-front.

The -1xI is handled separately, using a second call to int(). I couldn't figure out how to avoid this without costing more bytes than I saved.

def g(s):u=7<len(s)<10and sum(x*int(('0'+s)[-x])for x in range(10))-2*int(s[-1]);print(u%11<1)*u would work just as well, since it would add 1 times s[-1] but then subtract it twice, and it would also add 0 times (something) which of course wouldn't affect the sum.

Answer 19

Brain-Flak, 345 Bytes

Includes +3 for -a

([]){{}({}[((((()()()){}){}){}){}]<>)<>([])}{}<>([][(()()()()){}]){({}[()]){([]){{}{}([])}}}{}([{}])({}({}){})({}({})({}){})({}(({}){}){})({}(({})({})){}{})({}(({})({}){}){})({}((({}))({}){}){}{})({}((({}){}){}){})(({}(((({})){}){}){}{}{}<(((()()())()){}{})>)){{}({}(<>))<>{(({})){({}[()])<>}{}}{}<>([{}()]{}[{}]<(())>){((<{}{}>))}{}(<()>)}{}

Truthy is 1, Falsy has a 0 on the top of the stack.

Try it Online!

I'm pretty sure there is a shorter way to do the multiplication in a loop, but I haven't found it yet.

#reverse and subtract 48 from all numbers (ASCII -> decimal)
([]){{}({}[((((()()()){}){}){}){}]<>)<>([])}{}<> 

([][(()()()()){}])       #height - 8
{({}[()]){               #if not 0 subtract 1
   ([]){{}{}([])}        #if still not 0 pop everything
}}{}                     #this loop pops everything unless there are 8 or 9 digits

([{}])                   # -I
({}({}){})               # H*2
({}({})({}){})           # G*3
({}(({}){}){})           # F*4
({}(({})({})){}{})       # E*5
({}(({})({}){}){})       # D*6
({}((({}))({}){}){}{})   # C*7
({}((({}){}){}){})       # B*8
(({}(((({})){}){}){}{}{} # A*9 pushed twice with:
<(((()()())()){}{})>))   # 11 under it


{{} #if not 0
({}(<>))<>{(({})){({}[()])<>}{}}{}<>([{}()]{}   # mod 11
[{}]<(())>){((<{}{}>))}{}                       # logical not
(<()>)                                          # push 0 to exit loop
}{}
                                                # implicit print

Answer 20

C#, 120 115 bytes

This loops through the char[] it receives as input and returns true or false:

bool b(char[]n){int r=0,k,i=0,l=n.Length;for(;i<l;i++){k=i==l-1?-1:l-i;r+=k*(n[i]-48);}return r>0&r%11<1&l<10&l>7;}

Fiddle: https://dotnetfiddle.net/3Kaxrt

I'm sure I can scrape out a few bytes, especially in the messy return. Any ideas welcome!

Edit: Saved 5 bytes thanks to Kevin. I had no idea I could use & instead of &&!

Answer 21

PHP, 86 85 84 83 82 79 bytes

Note: uses PHP 7.1 for negative string indices.

for($l=log10($a=$argn);~$c=$a[-++$x];)$s+=$x>1?$x*$c:-$c;echo$s%11<1&$l>7&$l<9;

Run like this:

echo 010464554 | php -nR 'for($l=log10($a=$argn);~$c=$a[-++$x];)$s+=$x>1?$x*$c:-$c;echo$s%11<1&$l>7&$l<9;';echo
> 1

Version for PHP < 7.1 (+10 bytes)

echo 010464554 | php -nR 'for($l=log10($a=$argn);~$c=$a[strlen($a)-++$x];)$s+=$x>1?$x*$c:-$c;echo$s%11<1&$l>7&$l<9;';echo

Explanation

for(
  $l=log10(         # Take the log of the input number.
    $a=$argn        # Set input to $a
  );
  ~$c=$a[-++$x];    # Iterate over digits of input (reverse). Negate to
                    # change every char to extended ASCII (all truthy),
                    # without changing empty sting (still falsy, ending
                    # the loop).
)
  $s+=$x>1?         # Add current char to the sum...
     ?$x*$c:-$c;    # multiplied by $x, unless $x is 1; subtract it.
echo
  $s%11<1 &         # Check if sum is divisible by 11, and
  $l>7   &          # log of the input is greater than 7, and
  $l<9;             # log of the input is less than 9. Outputs 0 or 1.

Tweaks

• Shorter way to distinguish between empty string and "0", saved a byte
• Since 10000000 is invalid, no need to compare with greater than or equals, greater than suffices, saving a byte
• Shorter way to subtract least significant digit
• Negate char instead of XOR, saving a byte
• Saved 3 bytes by using -R to make $argn available

Answer 22

Java 8, 115 98 94 bytes

b->{int l=b.length,i=l,r=0;for(;l>7&l<10&i-->0;)r-=(b[i]-48)*(l-i<2?1:i-l);return r>0&r%11<1;}

I'm surprised no one has posted a Java answer yet, so here is one.

-4 bytes thanks to @ceilingcat.

Explanation:

Try it here.

b->{                // Method with character-array as parameter and boolean return-type
  int l=b.length,   //  Length of the array
      i=l,          //  Index-integer, starting at this length
      r=0;          //  The result-sum, starting at 0
  for(;l>7&l<10     //  Start looping if the length is either 8 or 9
       &i-->0;)     //  And continue looping downwards while the index is larger than 0
      r-=           //   Decrease the result-sum by:
         (b[i]-48)  //    The current digit
         *(         //    Multiplied by:
           l-i<2?   //     If `l-i` is 1:
            1       //      Simply multiply by 1
           :        //     Else:
            i-l);   //      Multiply by `i-l`
  return r>0        //  Return if the result-sum is larger than 0,
    &r%11<1;}       //   and if the result-sum is divisible by 11

Answer 23

Ly, 58 bytes

iy9L[r'0r!]ppry9=[pp8[f'0-srlrpsrl`*r,]p'0-N&+[92+%!u;]]u;

Try it online!

I thought this would be shorter... There's probably room for improvement?

First part, input digits, pad with leading 0 if necessary

i              - input all digits (as codepoints)
 y             - push the stack size onto the stack
  9L[    !]p   - if/then block, true if <9 digits
     r'0r      - reverse stack, push 0, reverse again
            p  - pop the stack size entry off the stack

Second part, only process digits if we end up with 9 digits

r              - reverse the stack
 y             - push the stack size info the stack
  9=[pp ... ]  - if/then block, true if stack size is 9

Third part, process the first 8 digits

8[               ,]p - loop 8 times
  f                  - bring digit forward
   '0-               - convert from char to int
      s              - save digit value
       rl            - copy digit to bottom of stack
         rp          - delete from top of stack
           s         - save current loop var
            rl       - copy to bottom of stack
              `      - increment by one
               *     - multiple with current digit
                r    - reverse stack

Fourth part, process last digit, sum results

'0-     - convert digit from char to int
   N    - negate
    &+  - sum all entries on the stack

Fifth part, "is it zero?" and "is divisible by 11?" checks

[       ]   - if/then block, true is sum is non-zero
 92+        - push 11 onto the stack
    %!      - modulo math to get remainder, invert the result
      u;    - print top of stack as int, then exit

Last part, prints "falsey" if some success criteria wasn't met

u;  - print top of stack (which will be 0) and exit

AWK, 88 bytes

$0="0"$0,n=gsub(a," ")-1{b=n-9;c=9}!b||b==1{for(d-=$n;++b<n;e=d%11)d+=$b*c--}1,$0=!e*!!d

Try it online!

And one I had fun golfing, just to abuse the flexibility of AWK.

$0="0"$0                             - append "0" to the input
           gsub(a," ')-1             - re-parse the input, one char per arg
        ,n=           -1             - set "n", decr RC to get number of chars
                        {         }  - code block...
                         b=n-9;      - set "b" to first char to use
                               c=9   - set "c" to initial multiplier val

!b||b==l                                   - true is we got 8 or 9 chars
        {                                } - code block...
         for(                  )           - loop over initial 8 chars
             d-=$n;                        - init: "d" set to neg of last digit
                   ++b<n;                  - test: ends after 8 chars processed
                         e=d%11            - loop-end: "e" is remainder of "%11"
                                d+=$b*c--  - loop-code: multiply and add next digit

1,           - unconditionally run implicit "print $0" code block
  $0=!e*!!d  - "$0" is 1 if accum value is non-zero and divisible by 11

Answer 24

K (ngn/k), 42 41 bytes

-1 byte from @ngn's improvements

{(4=-2!#x)&t&~11!t:+/(|-1,2+!8)*-9#0,.'x}

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Takes the input as a list of characters.

• .'x convert each digit to its integer (e.g. convert "123" to 1 2 3)
• -9#0, prepend a 0, then take the last nine values (handles padding 8-digit codes, and avoids errors on input that is not 9 digits long)
• (|-1,2+!8)* generate 9 8 7 6 5 4 3 2 -1, and multiply the parsed digits by this
• t:+/ take the sum, storing in variable t
• t&~11!t check that 11 evenly divides t, and that t is non-zero
• (4=-2!#x)& also check that the input is 8 or 9 characters long (literally: the length of the input (integer) divided by 2 is equal to 4)

Answer 25

Ruby, 65 bytes

-1 byte thanks to Kevin Cruijssen

->n{a,*b=n.to_i.digits
i=1
b[6]&&(b[..7].sum{_1*i+=1}-a)%11<1||p}

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Answer 26

Clojure, 114 bytes

Well this is something, - substracts the rest of the arguments from the first one so that handles the special case of weight -1. This function returns nil for inputs of invalid length, but on if clauses they operate the same as false. (#{8 9}(count v)) returns nil if length of v is not 8 or 9.

(fn[v](if(#{8 9}(count v))(#(and(< % 0)(=(mod % 11)0))(apply -(map *(range 1 10)(reverse(map #(-(int %)48)v)))))))

Test cases:

(pprint (group-by f (map str [123456782 232262536 "010464554" 10464554 44016773 "000000000" 192837465 247594057 88888888 73 3112223342 "000000012"])))
{true  ["123456782" "232262536" "010464554" "10464554" "44016773"],
 false ["000000000" "192837465" "247594057" "88888888" "000000012"],
 nil   ["73" "3112223342"]}

Answer 27

Perl 5, 63 + 2 (-F) = 65 bytes

$F[-1]*=-1;map$s+=++$i*$_,reverse@F;say/^.{8,9}$/&&$s&&!($s%11)

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Answer 28

Stax, 23 bytes

╪╦µΘç}<╔▼◘╞i∟~¿≥←║▐√ 4u

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Explanation

Uses the unpacked version to explain.

i%8A:byr{]ei^*mBN+|+c11%!L|A
i                               Suppress implicit eval
 %8A:b                          Length is 8 or 9 (Element #1 on the final stack)
      yr                        Reverse input
        {     m                 Map each element with
         ]e                         Its numerical value
           i^*                      Multiplied current 1-based loop index
               BN+              Negate the first element
                  |+            Sum (Element #2 on the final stack)
                    c11%!       Sum is multiple of 11 (Element #3 on the final stack)
                         L|A    Collect all the three elements and `and` them.

Answer 29

Python 3.8, 96 bytes

lambda i:7<len(i)<10*((S:=sum(a*b for a,b in zip([-1,*range(2,10)],map(int,i[::-1]))))%11<1)*S>0

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Similar to @TFeld's Python 2 answer, but uses Python 3.8 assignment expressions and a few other tricks to get it down to 96 bytes.

Answer 30

TI-Basic, 60 bytes

max(length(Ans)={8,9})sum(seq(int(10fPart(expr(Ans)/₁₀^(I)))(I-2(I=1)),I,1,9
not(fPart((Ans+not(Ans))/11

Takes input in Ans as a string. Output is stored in Ans and is displayed.