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  1. ; euler's sum of products conjecture
  2.  
  3. (define (euler n) ; brute force
  4.   (do ((e 5 (+ e 1))) ((= e n))
  5.     (do ((d (- e 1) (- d 1))) ((zero? d))
  6.       (do ((c (- d 1) (- c 1))) ((zero? c))
  7.         (do ((b (- c 1) (- b 1))) ((zero? b))
  8.           (do ((a (- b 1) (- a 1))) ((zero? a))
  9.             (when (= (+ (expt a 5) (expt b 5)
  10.                         (expt c 5) (expt d 5))
  11.                      (expt e 5))
  12.               (display a) (display "^5 + ")
  13.               (display b) (display "^5 + ")
  14.               (display c) (display "^5 + ")
  15.               (display d) (display "^5 = ")
  16.               (display e) (display "^5")
  17.               (newline))))))))
  18. (euler 145)
  19.  
  20. (define (euler n) ; cache powers
  21.   (let ((cache (make-vector n)))
  22.     (do ((i 1 (+ i 1))) ((= i n))
  23.       (vector-set! cache i (expt i 5)))
  24.     (do ((e 5 (+ e 1))) ((= e n))
  25.       (do ((d (- e 1) (- d 1))) ((zero? d))
  26.         (do ((c (- d 1) (- c 1))) ((zero? c))
  27.           (do ((b (- c 1) (- b 1))) ((zero? b))
  28.             (do ((a (- b 1) (- a 1))) ((zero? a))
  29.               (when (= (+ (vector-ref cache a)
  30.                           (vector-ref cache b)
  31.                           (vector-ref cache c)
  32.                           (vector-ref cache d))
  33.                        (vector-ref cache e))
  34.                 (display a) (display "^5 + ")
  35.                 (display b) (display "^5 + ")
  36.                 (display c) (display "^5 + ")
  37.                 (display d) (display "^5 = ")
  38.                 (display e) (display "^5")
  39.                 (newline)))))))))
  40. (euler 145)
  41.  
  42. (define (euler n) ; short-circuit loops
  43.   (let ((cache (make-vector n)))
  44.     (do ((i 1 (+ i 1))) ((= i n))
  45.       (vector-set! cache i (expt i 5)))
  46.     (do ((e 5 (+ e 1))) ((= e n))
  47.       (list-of (list a b c d e)
  48.         (d range (- e 1) 0)
  49.         (c range (- d 1) 0)
  50.         (c-sum is
  51.           (+ (vector-ref cache c)
  52.              (vector-ref cache d)))
  53.         (< c-sum (vector-ref cache e))
  54.         (b range (- c 1) 0)
  55.         (b-sum is
  56.           (+ c-sum
  57.              (vector-ref cache b)))
  58.         (< b-sum (vector-ref cache e))
  59.         (a range (- b 1) 0)
  60.         (= (+ b-sum (vector-ref cache a))
  61.            (vector-ref cache e))
  62.         (display a) (display "^5 + ")
  63.         (display b) (display "^5 + ")
  64.         (display c) (display "^5 + ")
  65.         (display d) (display "^5 = ")
  66.         (display e) (display "^5")
  67.         (newline)))))
  68. (euler 145)
Time limit exceeded #stdin #stdout 15s 9832KB
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https://ideone.com/RVcDBZ
language:
Scheme (guile 2.2.4)
created:
9 years ago
visibility:
secret

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