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-- erwin org. recursive func
CREATE OR REPLACE FUNCTION word_permutations(_word text)
RETURNS SETOF text
LANGUAGE plpgsql IMMUTABLE PARALLEL SAFE STRICT AS
$func$
BEGIN
IF length(_word) > 1 THEN
RETURN QUERY
SELECT left(_word, 1) || s || w
FROM (VALUES (''), (' ')) sep(s)
, word_permutations(right(_word, -1)) w;
ELSE
RETURN NEXT _word;
END IF;
END
$func$;
SELECT word_permutations('ABCD');
✓
word_permutations
ABCD
A BCD
AB CD
A B CD
ABC D
A BC D
AB C D
A B C D
…
hidden batch(es)
-- ypercube's recursive func
CREATE OR REPLACE FUNCTION word_permutations_yper(_word text)
RETURNS SETOF text
LANGUAGE plpgsql IMMUTABLE PARALLEL SAFE STRICT AS
$func$
declare
world_length int := length(_word);
BEGIN
IF world_length > 1 THEN
RETURN QUERY
SELECT wl || s || wr
FROM (VALUES (''), (' ')) sep(s)
, word_permutations(left(_word, world_length/2)) wl -- call to erwin func
, word_permutations(right(_word, -(world_length/2))) wr;
ELSE
RETURN NEXT _word;
END IF;
END
$func$;
SELECT word_permutations_yper('ABCD');
✓
word_permutations_yper
ABCD
AB CD
A BCD
A B CD
ABC D
AB C D
A BC D
A B C D
…
hidden batch(es)
-- optimized
CREATE OR REPLACE FUNCTION word_permutations2(_word text)
RETURNS SETOF text
LANGUAGE plpgsql IMMUTABLE PARALLEL SAFE STRICT AS
$func$
DECLARE
world_len int := length(_word);
BEGIN
CASE world_len
WHEN 2 THEN
RETURN NEXT _word;
RETURN NEXT OVERLAY(_word PLACING ' ' FROM 2 FOR 0);
WHEN 1, 0 THEN -- corner cases
RETURN NEXT _word;
ELSE
RETURN QUERY
SELECT wl || s || wr
FROM (VALUES (''), (' ')) sep(s)
, word_permutations2(left(_word, world_len/2)) wl
, word_permutations2(right(_word, -(world_len/2))) wr;
END CASE;
END
$func$;
SELECT word_permutations2('ABCD');
