TL;DR

Here we are with TASK #1 from The Weekly Challenge #177. Enjoy!

# The challenge

You are given a positive number, $n. Write a script to validate the given number against the included check digit. Please checkout the wikipedia page for information. Example 1 Input:$n = 5724
Output: 1 as it is valid number

Example 2

Input: $n = 5727 Output: 0 as it is invalid number # The questions If this were an interview question, Iâ€™d probably ask something about what weâ€™re supposed to validate and what would go beyond these boundaries. # The solution The Damm Algorithm is a way to calculate a control digit out of other digits. There are quite a few of these procedures, and it seems that this particular one has its own advantages, except - maybe - its reluctance on accepting leading 0, i.e. treating 1 and 0001 as if theyâ€™re the same thing. Which, honestly, they are - at least as long as we consider the input a positive number. In this challenge, it is. OK, this said, we have to play a treasure hunt onto a matrix. In Raku: #!/usr/bin/env raku use v6; sub MAIN ($input = 5724) { put damm-calculate($input) ?? 0 !! 1 } sub damm-calculate ($input) {
state @qs = <
0  3  1  7  5  9  8  6  4  2
7  0  9  2  1  5  4  8  6  3
4  2  0  6  8  7  1  3  5  9
1  7  5  0  9  8  3  4  2  6
6  1  2  3  0  4  5  9  7  8
3  6  7  4  2  0  9  5  8  1
5  8  6  9  7  2  0  1  3  4
8  9  4  5  3  6  2  0  1  7
9  4  3  8  6  1  7  2  0  5
2  5  8  1  4  3  6  7  9  0
>;
(0, $input.comb.Slip).reduce({@qs[10 *$^a + $^b]}); } I love reduce, as itâ€™s perfect for this kind of chain reaction stuff. We have to inject the equivalent of a leading 0 to get the ball started properly and focus on the first row at the beginning, but apart from this itâ€™s just the usual take result and new item, rinse, repeat. The matrix is represented as a linear array, as I like doing lately. Itâ€™s just for having some fun, I think some time ago I saw there is no real benefit in doing this. It does not improve readability, anyway, but might help keeping attention levels high with a little what the hell moment. I have to admit that I slapped the Slip without too much thinking. I donâ€™t know if Iâ€™m finally getting the gist of it, but Iâ€™ve been biten by the tightness of Raku containers many times and itâ€™s a sort of defensive attempt from my side. Punishment-based learning, if you will, although Iâ€™d like to use Slip and flat knowing better what they are for. Iâ€™ll get there, one day. The Perl counterpart is pretty much a translation with functions instead of methods. It kind of flows more naturally, although backwards, because it does not force the construction of a container of digits to ignite the process. This is such a subtle pet peeve that I have troubles understanding it, too. #!/usr/bin/env perl use v5.24; use warnings; use experimental 'signatures'; no warnings 'experimental::signatures'; use List::Util 'reduce'; my$input = shift // 5724;
say damm_calculate($input) ? 0 : 1; sub damm_calculate ($input) {
state $qs = [qw< 0 3 1 7 5 9 8 6 4 2 7 0 9 2 1 5 4 8 6 3 4 2 0 6 8 7 1 3 5 9 1 7 5 0 9 8 3 4 2 6 6 1 2 3 0 4 5 9 7 8 3 6 7 4 2 0 9 5 8 1 5 8 6 9 7 2 0 1 3 4 8 9 4 5 3 6 2 0 1 7 9 4 3 8 6 1 7 2 0 5 2 5 8 1 4 3 6 7 9 0 >]; reduce {$qs->[10 * $a +$b]} 0, split m{}mxs, \$input;
}

And thatâ€™s all, folks!

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