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3_70.scm
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3_70.scm
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(load "3_55.scm")
(define (interleave s1 s2)
(if (stream-null? s1)
s2
(cons-stream (stream-car s1)
(interleave s2 (stream-cdr s1)))))
(define (display-stream s)
(stream-for-each display-line s))
(define (display-line x)
(newline)
(display x))
(define (scale-stream stream factor)
(stream-map (lambda (x) (* x factor)) stream))
(define (merge s1 s2)
(cond ((stream-null? s1) s2)
((stream-null? s2) s1)
(else
(let ((s1car (stream-car s1))
(s2car (stream-car s2)))
(cond ((< s1car s2car)
(cons-stream s1car (merge (stream-cdr s1) s2)))
((> s1car s2car)
(cons-stream s2car (merge s1 (stream-cdr s2))))
(else
(cons-stream s1car
(merge (stream-cdr s1)
(stream-cdr s2)))))))))
(define (merge-weighted s1 s2 weight)
(define (merge s1 s2)
(cond ((stream-null? s1) s2)
((stream-null? s2) s1)
(else
(let ((s1car (stream-car s1))
(s2car (stream-car s2)))
(if (< (weight s1car) (weight s2car))
(cons-stream (stream-car s1) (merge (stream-cdr s1) s2))
(cons-stream (stream-car s2) (merge s1 (stream-cdr s2))))))))
(merge s1 s2))
(define (weighted-pairs s t weight)
(cons-stream
(list (stream-car s) (stream-car t))
(merge-weighted
(stream-map (lambda (x) (list (stream-car s) x))
(stream-cdr t))
(weighted-pairs (stream-cdr s) (stream-cdr t) weight) weight)))
(define part-a (weighted-pairs integers integers (lambda (x) (+ (car x) (cadr x)))))
(define int-235 (stream-filter (lambda (x) (not (or (= (remainder x 2) 0)
(= (remainder x 3) 0)
(= (remainder x 5) 0))))
integers))
(define weight235 (lambda (x) (+ (* 2 (car x)) (* 3 (cadr x)) (* 5 (car x)))))
(define part-b (weighted-pairs int-235 int-235 weight235))