gistfile1.sql

DROP TABLE IF EXISTS t;
CREATE TABLE t (
    id  int PRIMARY KEY
    ,adj    int[]
);


INSERT INTO t VALUES
    (1, ARRAY[2,3,4,5])
    ,(2, ARRAY[1])
    ,(3, ARRAY[1,6])
    ,(4, ARRAY[1])
    ,(5, ARRAY[1,7])
    ,(6, ARRAY[3])
    ,(7, ARRAY[5]);

CREATE INDEX _idx_adj on t USING gin (adj);

WITH RECURSIVE r (id, adj, step) AS (
    SELECT
        *
        ,1
    FROM
        t
    WHERE
        id = 1
    UNION ALL
    SELECT
        t.*
        ,r.step + 1
    FROM
        t,r
    WHERE
        t.id = ANY(r.adj) AND step < 3
)
SELECT
    id
    ,array_agg(step)
FROM
    r
GROUP BY
    id
HAVING
    array_agg(step) = ARRAY[3]
;