```1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 ``` ```; closest pair, part 1 (define rand #f) (define randint #f) (let ((two31 #x80000000) (a (make-vector 56 -1)) (fptr #f)) (define (mod-diff x y) (modulo (- x y) two31)) ; generic version ; (define (mod-diff x y) (logand (- x y) #x7FFFFFFF)) ; fast version (define (flip-cycle) (do ((ii 1 (+ ii 1)) (jj 32 (+ jj 1))) ((< 55 jj)) (vector-set! a ii (mod-diff (vector-ref a ii) (vector-ref a jj)))) (do ((ii 25 (+ ii 1)) (jj 1 (+ jj 1))) ((< 55 ii)) (vector-set! a ii (mod-diff (vector-ref a ii) (vector-ref a jj)))) (set! fptr 54) (vector-ref a 55)) (define (init-rand seed) (let* ((seed (mod-diff seed 0)) (prev seed) (next 1)) (vector-set! a 55 prev) (do ((i 21 (modulo (+ i 21) 55))) ((zero? i)) (vector-set! a i next) (set! next (mod-diff prev next)) (set! seed (+ (quotient seed 2) (if (odd? seed) #x40000000 0))) (set! next (mod-diff next seed)) (set! prev (vector-ref a i))) (flip-cycle) (flip-cycle) (flip-cycle) (flip-cycle) (flip-cycle))) (define (next-rand) (if (negative? (vector-ref a fptr)) (flip-cycle) (let ((next (vector-ref a fptr))) (set! fptr (- fptr 1)) next))) (define (unif-rand m) (let ((t (- two31 (modulo two31 m)))) (let loop ((r (next-rand))) (if (<= t r) (loop (next-rand)) (modulo r m))))) (init-rand 19380110) ; happy birthday donald e knuth (set! rand (lambda seed (cond ((null? seed) (/ (next-rand) two31)) ((eq? (car seed) 'get) (cons fptr (vector->list a))) ((eq? (car seed) 'set) (set! fptr (caadr seed)) (set! a (list->vector (cdadr seed)))) (else (/ (init-rand (modulo (numerator (inexact->exact (car seed))) two31)) two31))))) (set! randint (lambda args (cond ((null? (cdr args)) (if (< (car args) two31) (unif-rand (car args)) (floor (* (next-rand) (car args))))) ((< (car args) (cadr args)) (let ((span (- (cadr args) (car args)))) (+ (car args) (if (< span two31) (unif-rand span) (floor (* (next-rand) span)))))) (else (let ((span (- (car args) (cadr args)))) (- (car args) (if (< span two31) (unif-rand span) (floor (* (next-rand) span)))))))))) (define max-coord 1000000) (define (rand-points n) (define (r) (randint max-coord)) (do ((n n (- n 1)) (ps (list) (cons (cons (r) (r)) ps))) ((zero? n) ps))) (define (dist p q) (define (square x) (* x x)) (sqrt (+ (square (- (car p) (car q))) (square (- (cdr p) (cdr q)))))) (define (closest-pair ps) (let ((min-dist (* max-coord max-coord)) (min-pair (list))) (do ((ps ps (cdr ps))) ((null? (cdr ps))) (do ((qs (cdr ps) (cdr qs))) ((null? qs)) (let ((d (dist (car ps) (car qs)))) (when (< d min-dist) (set! min-dist d) (set! min-pair (cons (car ps) (list (car qs)))))))) (values min-dist min-pair))) (define points (rand-points 10)) (for-each (lambda (p) (display p) (newline)) points) (newline) (call-with-values (lambda () (closest-pair points)) (lambda (min-dist min-pair) (display min-dist) (newline) (display min-pair) (newline))) ```
 ```1 2 3 4 5 6 7 8 9 10 11 12 13 ``` ```(55898 . 311250) (970699 . 38095) (632947 . 399788) (894419 . 551994) (301018 . 725693) (226214 . 632064) (448323 . 874999) (712382 . 815609) (781530 . 304574) (388790 . 275421) 119841.6791312605 ((301018 . 725693) (226214 . 632064)) ```