26 lines
756 B
Racket
26 lines
756 B
Racket
#lang racket
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(require data/bit-vector)
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(define (quadruples top)
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(define top+1 (add1 top))
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(define 1..top (in-range 1 top+1))
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(define r (make-bit-vector top+1))
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(define ab (make-bit-vector (add1 (sqr (* top 2)))))
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(for* ((a 1..top) (b (in-range a top+1))) (bit-vector-set! ab (+ (sqr a) (sqr b)) #t))
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(for/fold ((s 3))
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((c 1..top))
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(for/fold ((s1 s) (s2 (+ s 2)))
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((d (in-range (add1 c) top+1)))
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(when (bit-vector-ref ab s1)
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(bit-vector-set! r d #t))
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(values (+ s1 s2) (+ s2 2)))
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(+ 2 s))
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(for/list ((i (in-naturals 1)) (v (in-bit-vector r 1)) #:unless v) i))
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(define (report n)
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(printf "Those values of d in 1..~a that can't be represented: ~a~%" n (quadruples n)))
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(report 2200)
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