1 files changed, 65 insertions, 0 deletions
diff --git a/challenge-211/luca-ferrari/postgresql/ch-2.sql b/challenge-211/luca-ferrari/postgresql/ch-2.sql
new file mode 100644
index 0000000000..802a8f6932
--- /dev/null
+++ b/challenge-211/luca-ferrari/postgresql/ch-2.sql
@@ -0,0 +1,65 @@
+--
+-- Perl Weekly Challenge 211
+-- Task 2
+--
+-- See <https://perlweeklychallenge.org/blog/perl-weekly-challenge-211/>
+--
+
+CREATE SCHEMA IF NOT EXISTS pwc211;
+
+-- see <https://wiki.postgresql.org/wiki/Permutations>
+CREATE FUNCTION pwc211.permute(anyarray)
+  RETURNS SETOF anyarray
+  LANGUAGE SQL IMMUTABLE
+AS $f$
+  SELECT (WITH RECURSIVE r(n,p,a,b)
+               AS (SELECT i, $1[1:0], $1, array_upper($1,1)
+                   UNION ALL
+                   SELECT n / b, p || a[n % b + 1], a[1:n % b] || a[n % b + 2:b], b-1
+                     FROM r
+                    WHERE b > 0)
+          SELECT p FROM r WHERE b=0)
+  FROM generate_series(0,factorial( (array_upper($1,1)) )::integer-1) i;
+$f$;
+
+
+
+
+CREATE OR REPLACE FUNCTION
+pwc211.task2_plpgsql( a int[] )
+RETURNS SETOF int[]
+AS $CODE$
+DECLARE
+	split_at int := 0;
+	current_array int[];
+	l int[];
+	r int [];
+	avg_l numeric;
+	avg_r numeric;
+BEGIN
+	split_at := array_length( a, 1 ) / 2;
+
+	FOR current_array IN SELECT * FROM pwc211.permute( a ) LOOP
+	    l := current_array[ 1:split_at ];
+	    r := current_array[ (split_at + 1): array_length( a, 1 ) ];
+
+
+	    SELECT avg( v )
+	    INTO   avg_l
+	    FROM   unnest( l ) v;
+
+	    SELECT avg( v )
+	    INTO   avg_r
+	    FROM   unnest( r ) v;
+
+	    IF avg_r = avg_l THEN
+	       RETURN NEXT l;
+	       RETURN NEXT r;
+	       RETURN;
+	    END IF;
+	END LOOP;
+
+RETURN;
+END
+$CODE$
+LANGUAGE plpgsql;