Scheme, pasted on Feb 5:
 ```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 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 ``` ```; two stream selection questions (define (range . args) (case (length args) ((1) (range 0 (car args) (if (negative? (car args)) -1 1))) ((2) (range (car args) (cadr args) (if (< (car args) (cadr args)) 1 -1))) ((3) (let ((le? (if (negative? (caddr args)) >= <=))) (let loop ((x(car args)) (xs '())) (if (le? (cadr args) x) (reverse xs) (loop (+ x (caddr args)) (cons x xs)))))) (else (error 'range "unrecognized arguments")))) (define sort #f) (define merge #f) (let () (define dosort (lambda (pred? ls n) (if (= n 1) (list (car ls)) (let ((i (quotient n 2))) (domerge pred? (dosort pred? ls i) (dosort pred? (list-tail ls i) (- n i))))))) (define domerge (lambda (pred? l1 l2) (cond ((null? l1) l2) ((null? l2) l1) ((pred? (car l2) (car l1)) (cons (car l2) (domerge pred? l1 (cdr l2)))) (else (cons (car l1) (domerge pred? (cdr l1) l2)))))) (set! sort (lambda (pred? l) (if (null? l) l (dosort pred? l (length l))))) (set! merge (lambda (pred? l1 l2) (domerge pred? l1 l2)))) (define (uniq-c eql? xs) (if (null? xs) xs (let loop ((xs (cdr xs)) (prev (car xs)) (k 1) (result '())) (cond ((null? xs) (reverse (cons (cons prev k) result))) ((eql? (car xs) prev) (loop (cdr xs) prev (+ k 1) result)) (else (loop (cdr xs) (car xs) 1 (cons (cons prev k) result))))))) (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 (select-equal xs) (let loop ((n 1) (x #f) (xs xs)) (cond ((null? xs) x) ((< (rand) (/ n)) (loop (+ n 1) (car xs) (cdr xs))) (else (loop (+ n 1) x (cdr xs)))))) (display (select-equal '(A D F A G))) (newline) (newline) (define (select-weighted xs) (let loop ((n 0) (x #f) (xs xs)) (if (null? xs) x (let ((y (caar xs))) (if (< (rand) (/ y (+ n y))) (loop (+ n y) (cadar xs) (cdr xs)) (loop (+ n y) x (cdr xs))))))) (display (select-weighted '((1 A) (2 D) (5 F) (3 A) (9 G)))) (newline) (newline) (define (symbolstring a) (symbol->string b))) (define (symbol=? a b) (string=? (symbol->string a) (symbol->string b))) (define (count n select input) (uniq-c symbol=? (sort symbol

Output:
 ```1 2 3 4 5 6 7 8 9 10 11 12 13 ``` ```A G A 20095 D 9840 F 10119 G 9946 A 40273 D 20134 F 49914 G 89679 ```