# Perl Weekly Challenge 177: damn numbers!

It is sad that, after more than three years of me doing Raku, I still don’t have any production code project to work on. Therefore, in order to keep my coding and Raku-ing (is that a term?) knowdledge, I try to solve every Perl Weekly Challenge tasks.

In the following, the assigned tasks for Challenge 177.

and for the sake of some Perl 5, let’s do some stuff also in PostgreSQL Pl/Perl:
Last, the solutions in PostgreSQL PL/PgSQL:

## PWC 177 - Task 1

Implement a Damn aghoritm checker, an application that can check if a number is correct using the Damn alghoritm, that is built on top of a permutation table.

``````sub MAIN( Int \$number-to-check, Bool :\$verbose = True ) {

my @check-table =
[ 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 ];

my \$interim = 0;

my @digits = \$number-to-check.comb;
my \$check-digit = @digits[ * - 1 ];

"Number \$number-to-check will be checked as { @digits.join } against check digit \$check-digit".say if \$verbose;

for @digits -> \$column {
"Digit \$column (column) with interim (row) \$interim => { @check-table[ \$interim ][\$column]}".say if \$verbose;
\$interim = @check-table[ \$interim ][\$column];
}

"Number \$number-to-check with last interim is \$interim".say if \$verbose;
'1'.say and exit if \$interim == 0;
'0'.say;

}

``````

Once you have the table, the alghoritm is quite simple: iterate over the table entries depending on every digit you get at every step. If the final result is zero, the number is correct.

## PWC 177 - Task 2

Find cyclop palindromes, those palindrome numbers that have a zero in the middle.

``````sub MAIN( int \$limit = 20 ) {

my @cyclops = lazy gather {
for 100 .. Inf {
# skip numbers that have not an odd count of digits
next if \$_.Str.chars %% 2;

# skip if the number does not have a middle zero
next if \$_.comb[ ( \$_.Str.chars / 2 ).Int ] != 0;

# skip if it is not palindrome
next if \$_.Str != \$_.Str.flip;

take \$_;
}
};

@cyclops[ 0 .. \$limit ].join( "\n" ).say;

}

``````

The idea is simple: for evrey number I produce I do skip non palindrome ones, those that do not have a zero in the middle of their digits, and those that have an even number of digits.

## PWC 177 - Task 1 in PostgreSQL PL/Perl

Very similar solution to the Raku one:

``````CREATE OR REPLACE FUNCTION
RETURNS BOOLEAN
AS \$CODE\$

my ( \$number_to_check ) = @_;
my \$check_table = [
[ 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 ]
];

my \$interim = 0;

for my \$column ( split( //, \$number_to_check ) ) {
\$interim = \$check_table->[ \$interim ][ \$column ];
}

return 1 if \$interim == 0;
return 0;

\$CODE\$
LANGUAGE plperl;

``````

## PWC 177 - Task 2 in PostgreSQL PL/Perl

A reimplementation of the Raku approach:

``````CREATE OR REPLACE FUNCTION
RETURNS SETOF INT
AS \$CODE\$

my ( \$limit ) = @_;

for my \$current ( 100 .. 999999 ) {
next if length( \$current ) % 2 == 0;
next if \$current != reverse( \$current );
next if ( split( //, \$current) )[ length( \$current ) / 2 ] != 0;

\$limit-- and return_next( \$current );
last if \$limit <= 0;
}

return undef;

\$CODE\$
LANGUAGE plperl;

``````

## PWC 177 - Task 1 in PostgreSQL PL/PgSQL

Here I use a temporary table to store the interim values for the check table. Yeah, filling in the table is boring, but once it is done, the function can reduce its core at a few lines.
I decided to use a `TEMPORARY TABLE` to store the values, indexing them by rown and column so that the subsequent selection will result easier. The table has the clause `ON COMMIT DROP` that means it will be deleted once the function (that runs in a transaction) ends.

``````CREATE OR REPLACE FUNCTION
pwc177.task1_plpgsql( n int )
RETURNS BOOLEAN
AS \$CODE\$
DECLARE
interim int := 0;
col     int := 0;
BEGIN

CREATE TEMPORARY TABLE
t_check( r int, c int, v int )
ON COMMIT DROP;

INSERT INTO t_check( r, c, v )
VALUES
( 0, 0, 0),
( 0, 1,  3),
( 0, 2,  1),
( 0, 3, 7),
( 0, 4, 5),
( 0, 5, 9),
( 0, 6, 8),
( 0, 7, 6),
( 0, 8, 4),
( 0, 9, 2),
( 1,0,  7),
( 1,1, 0),
( 1,2, 9),
( 1,3, 2),
( 1,4, 1),
( 1,5,  5),
( 1,6, 4),
( 1,7,  8),
( 1,8,  6),
( 1,9, 3),
( 2,0, 4),
( 2,1, 2),
( 2,2, 0),
( 2,3, 6),
( 2,4, 8),
( 2,5, 7),
( 2,6, 1),
( 2,7, 3),
( 2,8,  5),
( 2,9,  9),
( 3,0,  1),
( 3,1,  7),
( 3,2,   5),
( 3,3,  0),
( 3,4,  9),
( 3,5,  8),
( 3,6,  3),
( 3,7,  4),
( 3,8,   2),
( 3,9,  6),
( 4,0,  6),
( 4,1,  1),
( 4,2,  2),
( 4,3,  3),
( 4,4,  0),
( 4,5,  4),
( 4,6,  5),
( 4,7,  9),
( 4,8,  7),
( 4,9,  8),
( 5,0, 3),
( 5,1, 6),
( 5,2, 7),
( 5,3, 4),
( 5,4, 2),
( 5,5, 0),
( 5,6, 9),
( 5,7, 5),
( 5,8, 8),
( 5,9, 1) ,
( 6,0, 5),
( 6,1, 8),
( 6,2, 6),
( 6,3, 9),
( 6,4, 7),
( 6,5, 2),
( 6,6, 0),
( 6,7, 1),
( 6,8, 3),
( 6,9, 4) ,
( 7,0, 8),
( 7,1, 9),
( 7,2, 4),
( 7,3, 5),
( 7,4, 3),
( 7,5, 6),
( 7,6, 2),
( 7,7, 0),
( 7,8, 1),
( 7,9, 7) ,
( 8,0, 9),
( 8,1, 4),
( 8,2, 3),
( 8,3, 8),
( 8,4, 6),
( 8,5, 1),
( 8,6, 7),
( 8,7, 2),
( 8,8, 0),
( 8,9, 5) ,
( 9,0,  2),
( 9,1,  5),
( 9,2,  8),
( 9,3,  1),
( 9,4,  4),
( 9,5,  3),
( 9,6,  6),
( 9,7,  7),
( 9,8,  9),
( 9,9,  0)
;

FOR col IN SELECT regexp_split_to_table( n::text, '' ) LOOP
SELECT v
INTO interim
FROM t_check
WHERE c = col
AND   r = interim;
END LOOP;

IF interim = 0 THEN
RETURN TRUE;
ELSE
RETURN FALSE;
END IF;

END
\$CODE\$
LANGUAGE plpgsql;

``````

The usage of `regexp_split_to_table` allows me to iterate quickly over the digits of the incoming number.

## PWC 177 - Task 2 in PostgreSQL PL/PgSQL

Similar implementation to the Raku solution, except that I use `reverse` to check if the number is palindrome and `substring` to get its midway digit (pay atetntion: in SQL strings starts at character `1`):

``````CREATE OR REPLACE FUNCTION
pwc177.task2_plpgsql( l int default 20 )
RETURNS SETOF INT
AS \$CODE\$
DECLARE
i int;
BEGIN
FOR i IN 100 .. 99999 LOOP
IF i::text <> reverse( i::text ) THEN
-- not palindrome
CONTINUE;
END IF;

IF length( i::text ) % 2 = 0 THEN
-- even length
CONTINUE;
END IF;

IF substring( i::text, length( i::text ) / 2 + 1, 1 ) <> '0' THEN
CONTINUE;
END IF;

RETURN NEXT i;
l := l - 1;
EXIT WHEN l = 0;

END LOOP;

RETURN;
END
\$CODE\$
LANGUAGE plpgsql;

``````

The article Perl Weekly Challenge 177: damn numbers! has been posted by Luca Ferrari on August 10, 2022