30 lines
1.1 KiB
Scheme
30 lines
1.1 KiB
Scheme
(import (scheme base)
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(scheme write))
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;; -- given two sets represented as lists, return (A \ B)
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(define (a-without-b a b)
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(cond ((null? a)
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'())
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((member (car a) (cdr a)) ; drop head of a if it's a duplicate
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(a-without-b (cdr a) b))
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((member (car a) b) ; head of a is in b so drop it
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(a-without-b (cdr a) b))
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(else ; head of a not in b, so keep it
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(cons (car a) (a-without-b (cdr a) b)))))
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;; -- given two sets represented as lists, return symmetric difference
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(define (symmetric-difference a b)
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(append (a-without-b a b)
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(a-without-b b a)))
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;; -- test case
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(define A '(John Bob Mary Serena))
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(define B '(Jim Mary John Bob))
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(display "A\\B: ") (display (a-without-b A B)) (newline)
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(display "B\\A: ") (display (a-without-b B A)) (newline)
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(display "Symmetric difference: ") (display (symmetric-difference A B)) (newline)
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;; -- extra test as we are using lists
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(display "Symmetric difference 2: ")
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(display (symmetric-difference '(John Serena Bob Mary Serena)
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'(Jim Mary John Jim Bob))) (newline)
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