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  1. ; rip leibniz
  2.  
  3. (define (range . args)
  4.   (case (length args)
  5.     ((1) (range 0 (car args) (if (negative? (car args)) -1 1)))
  6.     ((2) (range (car args) (cadr args) (if (< (car args) (cadr args)) 1 -1)))
  7.     ((3) (let ((le? (if (negative? (caddr args)) >= <=)))
  8.            (let loop ((x(car args)) (xs '()))
  9.              (if (le? (cadr args) x)
  10.                  (reverse xs)
  11.                  (loop (+ x (caddr args)) (cons x xs))))))
  12.     (else (error 'range "unrecognized arguments"))))
  13.  
  14. (define rand #f)
  15. (define randint #f)
  16. (let ((two31 #x80000000) (a (make-vector 56 -1)) (fptr #f))
  17.   (define (mod-diff x y) (modulo (- x y) two31)) ; generic version
  18.   ; (define (mod-diff x y) (logand (- x y) #x7FFFFFFF)) ; fast version
  19.   (define (flip-cycle)
  20.     (do ((ii 1 (+ ii 1)) (jj 32 (+ jj 1))) ((< 55 jj))
  21.       (vector-set! a ii (mod-diff (vector-ref a ii) (vector-ref a jj))))
  22.     (do ((ii 25 (+ ii 1)) (jj 1 (+ jj 1))) ((< 55 ii))
  23.       (vector-set! a ii (mod-diff (vector-ref a ii) (vector-ref a jj))))
  24.     (set! fptr 54) (vector-ref a 55))
  25.   (define (init-rand seed)
  26.     (let* ((seed (mod-diff seed 0)) (prev seed) (next 1))
  27.       (vector-set! a 55 prev)
  28.       (do ((i 21 (modulo (+ i 21) 55))) ((zero? i))
  29.         (vector-set! a i next) (set! next (mod-diff prev next))
  30.         (set! seed (+ (quotient seed 2) (if (odd? seed) #x40000000 0)))
  31.         (set! next (mod-diff next seed)) (set! prev (vector-ref a i)))
  32.       (flip-cycle) (flip-cycle) (flip-cycle) (flip-cycle) (flip-cycle)))
  33.   (define (next-rand)
  34.     (if (negative? (vector-ref a fptr)) (flip-cycle)
  35.       (let ((next (vector-ref a fptr))) (set! fptr (- fptr 1)) next)))
  36.   (define (unif-rand m)
  37.     (let ((t (- two31 (modulo two31 m))))
  38.       (let loop ((r (next-rand)))
  39.         (if (<= t r) (loop (next-rand)) (modulo r m)))))
  40.   (init-rand 19380110) ; happy birthday donald e knuth
  41.   (set! rand (lambda seed
  42.     (cond ((null? seed) (/ (next-rand) two31))
  43.           ((eq? (car seed) 'get) (cons fptr (vector->list a)))
  44.           ((eq? (car seed) 'set) (set! fptr (caadr seed))
  45.                                  (set! a (list->vector (cdadr seed))))
  46.           (else (/ (init-rand (modulo (numerator
  47.                   (inexact->exact (car seed))) two31)) two31)))))
  48.   (set! randint (lambda args
  49.     (cond ((null? (cdr args))
  50.             (if (< (car args) two31) (unif-rand (car args))
  51.               (floor (* (next-rand) (car args)))))
  52.           ((< (car args) (cadr args))
  53.             (let ((span (- (cadr args) (car args))))
  54.               (+ (car args)
  55.                  (if (< span two31) (unif-rand span)
  56.                    (floor (* (next-rand) span))))))
  57.           (else (let ((span (- (car args) (cadr args))))
  58.                   (- (car args)
  59.                      (if (< span two31) (unif-rand span)
  60.                        (floor (* (next-rand) span))))))))))
  61.  
  62. (define (shuffle x)
  63.   (do ((v (list->vector x)) (n (length x) (- n 1)))
  64.       ((zero? n) (vector->list v))
  65.     (let* ((r (randint n)) (t (vector-ref v r)))
  66.       (vector-set! v r (vector-ref v (- n 1)))
  67.       (vector-set! v (- n 1) t))))
  68.  
  69. (define (sorted lt? xs)
  70.   (let loop ((xs xs) (count 1))
  71.     (cond ((null? (cdr xs)) count)
  72.           ((lt? (car xs) (cadr xs))
  73.             (loop (cdr xs) (+ count 1)))
  74.           (else count))))
  75.  
  76. (define (comps n)
  77.   (let loop ((i n) (cnt 0))
  78.     (if (zero? i) cnt
  79.       (loop (- i 1)
  80.             (+ cnt (sorted < (shuffle (range n))))))))
  81.  
  82. (display (comps 100)) (newline)
Success #stdin #stdout 0.57s 9576KB
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https://ideone.com/vmiDIf
language:
Scheme (guile 2.2.4)
created:
7 years ago
visibility:
public

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