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1 point by cchooper 6083 days ago | link | parent

Getting shorter:

  (def rot ((x . y)) (join y `(,x)))

  (def nqueens (n)
    (withs (m (mod n 12) r (range 1 n) od (keep odd r) cod (cddr od) s '(1 3) ev (keep even r))
           (if (join (pos m '(3 9)) (rot ev) (join cod s))
               (join ev (case m 8 (apply join (map rev (pair od)))
                                2 (join (rev s) (rot cod))
                                od)))))
The things Arc is missing from Ruby are partition and testing against multiple objects in a case. With those it would become:

  (def rot ((x . y)) (join y `(,x)))

  (def nqueens (n)
    (withs ((od ev) (part odd (range 1 n)) cod (cddr od) s '(1 3))
           (join ev (case (mod n 12) 8    (apply join (map rev (pair od)))
                                     2    (join (rev s) (rot cod))
                                     3, 9 (do (zap (rot ev)) (join cod s))
                                     od))))