Created
February 28, 2018 07:40
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WITH RECURSIVE | |
tblidx AS ( | |
SELECT ROW_NUMBER() OVER() AS id, x, y | |
FROM tbl), | |
root AS ( | |
SELECT ROW_NUMBER() OVER() AS id, map.aid AS aid, map.bid AS bid, map.len AS len | |
FROM ( | |
SELECT a.id AS aid, b.id AS bid, | |
SQRT(POW(a.x-b.x,2)+POW(a.y-b.y,2)) AS len | |
FROM tblidx AS a | |
CROSS JOIN tblidx AS b | |
ORDER BY len | |
) AS map | |
), | |
kruskalinit(data, n) AS ( | |
VALUES(ARRAY[1], 1) | |
UNION ALL | |
SELECT data || n + 1, n + 1 | |
FROM kruskalinit | |
WHERE n < ( | |
SELECT COUNT(1) | |
FROM tblidx | |
) | |
), | |
kruskal(ans, tablex, n) AS ( | |
(SELECT 0 :: DOUBLE PRECISION, data, 1 | |
FROM kruskalinit | |
ORDER BY n DESC | |
LIMIT 1) | |
UNION ALL | |
SELECT | |
CASE WHEN tablex[root.aid] != tablex[root.bid] | |
THEN | |
ans + root.len | |
ELSE | |
ans | |
END, | |
(SELECT ARRAY_AGG( | |
CASE WHEN i = tablex[root.bid]::INTEGER | |
THEN | |
tablex[root.aid]::INTEGER | |
ELSE | |
i | |
END) | |
FROM (SELECT UNNEST(tablex) AS i) AS x), | |
n+1 | |
FROM kruskal, root | |
WHERE n <= (SELECT COUNT(1) FROM root) AND root.id = n | |
) | |
SELECT MAX(ans) AS c FROM kruskal; |
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