SICP 問題 4.39

制限の順番は解には影響しないが，その時間には影響する．
失敗が多い制限ほど先にテストするほうが実行速度は速くなる．

;; 本来のmultiple-dwelling
(define (multiple-dwelling)
  (let ((baker (amb 1 2 3 4 5))
        (cooper (amb 1 2 3 4 5))
        (fletcher (amb 1 2 3 4 5))
        (miller (amb 1 2 3 4 5))
        (sith (amb 1 2 3 4 5)))
    (require (distinct (list baker cooper fletcher miller smith)))
    (require (not (= baker 5)))
    (require (not (= cooper 1)))
    (require (not (= fletcher 5)))
    (require (not (= fletcher 1)))
    (require (< cooper miller))
    (require (not (= (abs (- smith fletcher)) 1)))
    (require (not (= (abs (- fletcher cooper)))))
    (list (list 'baker baker)
          (list 'cooper cooper)
          (list 'fletcher fletcher)
          (list 'miller miller)
          (list 'smith smith))))

;; 改良版
(define (multiple-dwelling)
  (let ((baker (amb 1 2 3 4 5))
        (cooper (amb 1 2 3 4 5))
        (fletcher (amb 1 2 3 4 5))
        (miller (amb 1 2 3 4 5))
        (sith (amb 1 2 3 4 5)))
    (require (distinct (list baker cooper fletcher miller smith)))
    (require (< cooper miller))
    (require (not (= (abs (- fletcher cooper)))))
    (require (not (= (abs (- smith fletcher)) 1)))
    (require (not (= fletcher 1)))
    (require (not (= fletcher 5)))
    (require (not (= baker 5)))
    (require (not (= cooper 1)))
    (list (list 'baker baker)
          (list 'cooper cooper)
          (list 'fletcher fletcher)
          (list 'miller miller)
          (list 'smith smith))))