26 lines
755 B
Plaintext
26 lines
755 B
Plaintext
;;
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;; using the native (combinations) function
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(lib 'list)
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(combinations (iota 5) 3)
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→ ((0 1 2) (0 1 3) (0 1 4) (0 2 3) (0 2 4) (0 3 4) (1 2 3) (1 2 4) (1 3 4) (2 3 4))
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;;
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;; using an iterator
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;;
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(lib 'sequences)
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(take (combinator (iota 5) 3) #:all)
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→ ((0 1 2) (0 1 3) (0 1 4) (0 2 3) (0 2 4) (0 3 4) (1 2 3) (1 2 4) (1 3 4) (2 3 4))
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;;
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;; defining a function
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;;
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(define (combine lst p) (cond
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[(null? lst) null]
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[(< (length lst) p) null]
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[(= (length lst) p) (list lst)]
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[(= p 1) (map list lst)]
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[else (append
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(map cons (circular-list (first lst)) (combine (rest lst) (1- p)))
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(combine (rest lst) p))]))
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(combine (iota 5) 3)
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→ ((0 1 2) (0 1 3) (0 1 4) (0 2 3) (0 2 4) (0 3 4) (1 2 3) (1 2 4) (1 3 4) (2 3 4))
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