Petar Kapriš
2ca5e73a27
Notes: The exercise 2.37 on Hexlet's site has an error, noted in the comments. Also, their page for exercise 2.38 should probably have 0 tests. And finally, I did not calculate the exact number in the final exercise 2.43, but I included a relevant discussion.
40 lines
No EOL
1.1 KiB
Scheme
40 lines
No EOL
1.1 KiB
Scheme
#lang sicp
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(define (accumulate op initial sequence)
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(if (null? sequence)
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initial
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(op (car sequence)
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(accumulate op initial (cdr sequence)))))
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(define (flatmap proc seq)
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(accumulate append nil (map proc seq)))
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(define (filter predicate sequence)
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(cond ((null? sequence) nil)
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((predicate (car sequence))
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(cons (car sequence)
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(filter predicate (cdr sequence))))
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(else (filter predicate (cdr sequence)))))
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(define (enumerate-interval a b)
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(if (> a b)
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'()
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(cons a (enumerate-interval (+ a 1) b))))
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(define (sum l) (accumulate + 0 l))
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; returns a function which checks given list for
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; specific sum
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(define (sum-is-num s)
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(lambda (list)
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(= (sum list) s)))
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(define (ordered-triples-with-sum n s)
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(filter (sum-is-num s)
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(flatmap (lambda (i)
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(flatmap (lambda (j)
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(map (lambda (k)
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(list i j k))
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(enumerate-interval 1 (- j 1))))
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(enumerate-interval 1 (- i 1))))
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(enumerate-interval 1 n)))) |