Perl Weekly Challenge 217: Did I misunderstand?

This post presents my solutions to the Perl Weekly Challenge 217.
I keep doing the Perl Weekly Challenge in order to mantain my coding skills in good shape, as well as in order to learn new things, with particular regard to Raku, a language that I love.
This week, I solved the following tasks:
The PL/Perl implementations are very similar to a pure Perl implementation, even if the PostgreSQL environment could involve some more constraints. Similarly, the PL/PgSQL implementations help me keeping my PostgreSQL programming skills in good shape.

Raku Implementations

PWC 217 - Task 1 - Raku Implementation

The first task was about to find the fourth element in a sorted matrix made of integers. As far as I understand from the examples, the matrix is flattened into an array, sorted naturally and then the fourth element is extracted. This made me implement it as an application accepting a flat array. 

sub MAIN( *@n where { @n.grep( * ~~ Int ).elems == @n.elems } ) {
    @n.sort()[ 3 ].say;
}


PWC 217 - Task 2 - Raku Implementation

Given a list of integers, find out their composition that provides the biggest integer as a result. 

sub MAIN( *@list where { @list.grep( * ~~ Int ).elems == @list.elems } ) {
    my $max = 0;
    for @list.permutations {
	   $max = $_.join if ( $_.join.Int > $max );
    }

    $max.say;
}


The idea is to search thru all the permutations of the input array, trying to see if the array can be joined into a $max value.

PL/Perl Implementations

PWC 217 - Task 1 - PL/Perl Implementation

If the function accepts the flattened matrix, its implementation is really simple: 

CREATE OR REPLACE FUNCTION
pwc217.task1_plperl( int[] )
RETURNS int
AS $CODE$
   my ( $array ) = @_;
   return ( sort( $array->@* ) )[ 3 ];
$CODE$
LANGUAGE plperl;


PWC 217 - Task 2 - PL/Perl Implementation

A all permutations based implementation, where I use the List::Permutor module and hence the plperlu untrusted language: 

CREATE OR REPLACE FUNCTION
pwc217.task2_plperl( int[] )
RETURNS int
AS $CODE$
   use List::Permutor;
   my ( $max ) = 0;
   my $engine = List::Permutor->new( $_[0]->@* );
   while ( my @current = $engine->next ) {
   	 $max = join( '', @current ) if ( join( '', @current ) > $max );
   }

   return $max;
$CODE$
LANGUAGE plperlu;


PostgreSQL Implementations

PWC 217 - Task 1 - PL/PgSQL Implementation

A single query in SQL: 

CREATE OR REPLACE FUNCTION
pwc217.task1_plpgsql( a int[] )
RETURNS int
AS $CODE$
   SELECT v
   FROM unnest( a ) v
   ORDER BY 1
   LIMIT 1
   OFFSET 3;
$CODE$
LANGUAGE sql;


The idea is to unnest the incoming array, making it a table, order the result by the values, get a single result at displacement 3.

PWC 217 - Task 2 - PL/PgSQL Implementation

Again, a single query implementation: 

CREATE OR REPLACE FUNCTION
pwc217.task2_plpgsql( a int[] )
RETURNS int
AS $CODE$
   SELECT string_agg( v.vv::text, '' )::int
   FROM ( SELECT vv
          FROM unnest( a ) vv
	  ORDER BY ( vv % 10 ) DESC  ) v;
$CODE$
LANGUAGE sql;


I unnest the array making it a table, and order the result by the remainder of 10. Then I aggregate the result into a single tring, that is then cast to an integer. This is not a perfect solution, since it assumes you don’t specify numbers greater than 10.

The article Perl Weekly Challenge 217: Did I misunderstand? has been posted by Luca Ferrari on May 15, 2023

Tags: raku , perlweeklychallenge , perl