Magic hexagram

magic-hexagram.scm

(use util.combinations)
(use gauche.collection)

; Magic hexagram
;
;       a
;      / \
; b---c---d---e
;  \ /     \ /
;   f       g
;  / \     / \
; h---i---j---k
;      \ / 
;       l

(define (nth lst n)
  (vector-ref (list->vector lst) n))

(permutations*-for-each 
  (lambda (lst)
    (let ((a (nth lst 0))
          (b (nth lst 1))
          (c (nth lst 2))
          (d (nth lst 3))
          (e (nth lst 4))
          (f (nth lst 5))
          (g (nth lst 6))
          (h (nth lst 7))
          (i (nth lst 8))
          (j (nth lst 9))
          (k (nth lst 10))
          (l (nth lst 11)))
      (when (= (+ a c f h)
               (+ e g j l)
               (+ b c d e)
               (+ h i j k)
               (+ a d g k)
               (+ b f i l))
        (print lst))))
  '(1 2 3 4 5 6 7 8 9 10 11 12))