33 lines
845 B
Racket
33 lines
845 B
Racket
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#! /usr/bin/racket
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#lang racket/base
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(define (square n)
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(* n n))
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(define (smallest-divisor n)
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(find-divisor n 2))
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(define (find-divisor n test-divisor)
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(define (next iterator)
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(if (= iterator 2) 3 (+ iterator 2)))
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(cond ((> (square test-divisor) n) n)
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((divides? test-divisor n) test-divisor)
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(else (find-divisor n (next test-divisor)))))
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(define (divides? a b)
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(= (remainder b a) 0))
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(define (prime? n)
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(= n (smallest-divisor n)))
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(define (filtered-accumulate combiner null-value predicate term a next b)
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(define (iter a result)
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(if (> a b)
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result
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(iter (next a) (combiner (if (predicate a) (term a) null-value) result))))
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(iter a null-value))
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(define (range-sum-of-primes a b)
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(filtered-accumulate + 0 prime? (lambda (x) x) a (lambda (x) (+ 1 x)) b))
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(range-sum-of-primes 2 10)
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