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  1. ; sum-of-perfect-powers
  2.  
  3. (define-syntax fold-of
  4.   (syntax-rules (range in is)
  5.     ((_ "z" f b e) (set! b (f b e)))
  6.     ((_ "z" f b e (v range fst pst stp) c ...)
  7.       (let* ((x fst) (p pst) (s stp)
  8.              (le? (if (positive? s) =)))
  9.         (do ((v x (+ v s))) ((le? p v) b)
  10.           (fold-of "z" f b e c ...))))
  11.     ((_ "z" f b e (v range fst pst) c ...)
  12.       (let* ((x fst) (p pst) (s (if (< x p) 1 -1)))
  13.         (fold-of "z" f b e (v range x p s) c ...)))
  14.     ((_ "z" f b e (v range pst) c ...)
  15.       (fold-of "z" f b e (v range 0 pst) c ...))
  16.     ((_ "z" f b e (x in xs) c ...)
  17.       (do ((t xs (cdr t))) ((null? t) b)
  18.         (let ((x (car t)))
  19.           (fold-of "z" f b e c ...))))
  20.     ((_ "z" f b e (x is y) c ...)
  21.       (let ((x y)) (fold-of "z" f b e c ...)))
  22.     ((_ "z" f b e p? c ...)
  23.       (if p? (fold-of "z" f b e c ...)))
  24.     ((_ f i e c ...)
  25.       (let ((b i)) (fold-of "z" f b e c ...)))))
  26.  
  27. (define-syntax list-of (syntax-rules ()
  28.   ((_ arg ...) (reverse (fold-of
  29.     (lambda (d a) (cons a d)) '() arg ...)))))
  30.  
  31. (define sort #f)
  32. (define merge #f)
  33. (let ()
  34.   (define dosort
  35.     (lambda (pred? ls n)
  36.       (if (= n 1)
  37.           (list (car ls))
  38.           (let ((i (quotient n 2)))
  39.             (domerge pred?
  40.                      (dosort pred? ls i)
  41.                      (dosort pred? (list-tail ls i) (- n i)))))))
  42.   (define domerge
  43.     (lambda (pred? l1 l2)
  44.       (cond
  45.         ((null? l1) l2)
  46.         ((null? l2) l1)
  47.         ((pred? (car l2) (car l1))
  48.          (cons (car l2) (domerge pred? l1 (cdr l2))))
  49.         (else (cons (car l1) (domerge pred? (cdr l1) l2))))))
  50.   (set! sort
  51.     (lambda (pred? l)
  52.       (if (null? l) l (dosort pred? l (length l)))))
  53.   (set! merge
  54.     (lambda (pred? l1 l2)
  55.       (domerge pred? l1 l2))))
  56.  
  57. (define (unique eql? xs)
  58.   (cond ((null? xs) '())
  59.         ((null? (cdr xs)) xs)
  60.         ((eql? (car xs) (cadr xs))
  61.           (unique eql? (cdr xs)))
  62.         (else (cons (car xs) (unique eql? (cdr xs))))))
  63.  
  64. (define sum-of-perfect-powers
  65.   (let ((xs (unique = (sort <
  66.          (list-of (expt x n)
  67.                   (x range 1 1001)
  68.                   (n range 2 20)
  69.                   (<= (expt x n) 1000000))))))
  70.     (lambda (x)
  71.       (let loop ((xs xs))
  72.         (if (null? xs) #f
  73.           (if (member (- x (car xs)) (cdr xs))
  74.               (list (car xs) (- x (car xs)))
  75.               (loop (cdr xs))))))))
  76.  
  77. (display (sum-of-perfect-powers 25)) (newline)
  78. (display (sum-of-perfect-powers 26)) (newline)
  79. (display (sum-of-perfect-powers 27)) (newline)
Success #stdin #stdout 0.42s 52848KB
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(9 16)
(1 25)
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https://ideone.com/K3wjrq
language:
Scheme (guile 2.2.4)
created:
5 years ago
visibility:
public

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