26 lines
877 B
Racket
26 lines
877 B
Racket
#lang racket
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(define the-tree ; Node: (list <data> <left> <right>)
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'(1 (2 (4 (7 #f #f) #f) (5 #f #f)) (3 (6 (8 #f #f) (9 #f #f)) #f)))
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(define (preorder tree visit)
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(let loop ([t tree])
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(when t (visit (car t)) (loop (cadr t)) (loop (caddr t)))))
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(define (inorder tree visit)
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(let loop ([t tree])
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(when t (loop (cadr t)) (visit (car t)) (loop (caddr t)))))
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(define (postorder tree visit)
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(let loop ([t tree])
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(when t (loop (cadr t)) (loop (caddr t)) (visit (car t)))))
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(define (levelorder tree visit)
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(let loop ([trees (list tree)])
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(unless (null? trees)
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((compose1 loop (curry filter values) append*)
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(for/list ([t trees] #:when t) (visit (car t)) (cdr t))))))
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(define (run order)
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(printf "~a:" (object-name order))
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(order the-tree (λ(x) (printf " ~s" x)))
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(newline))
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(for-each run (list preorder inorder postorder levelorder))
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