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  1. ; reverse vowels
  2.  
  3. (define (vowel? c) (member (char-downcase c) '(#\a #\e #\i #\o #\u)))
  4.  
  5. (define (reverse-vowels str)
  6.   (let* ((cs (string->list str)) (vs (reverse (filter vowel? cs))))
  7.     (let loop ((cs cs) (vs vs) (zs (list)))
  8.       (cond ((null? cs) (list->string (reverse zs)))
  9.             ((vowel? (car cs))
  10.               (let ((f (if (char-upper-case? (car cs)) char-upcase char-downcase)))
  11.                 (loop (cdr cs) (cdr vs) (cons (f (car vs)) zs))))
  12.             (else (loop (cdr cs) vs (cons (car cs) zs)))))))
  13.  
  14. (display (reverse-vowels "HELLO world")) (newline)
  15. (display (reverse-vowels "Programming PRAXIS")) (newline)
  16.  
  17. (define (reverse-vowels str)
  18.   (define (fix-case x y)
  19.     (if (char-upper-case? x)
  20.         (char-upcase y)
  21.         (char-downcase y)))
  22.   (let loop ((lo 0) (hi (- (string-length str) 1)))
  23.     (cond ((< hi lo) str)
  24.           ((and (vowel? (string-ref str lo))
  25.                 (vowel? (string-ref str hi)))
  26.             (let ((temp (string-ref str lo)))
  27.                (string-set! str lo
  28.                  (fix-case temp (string-ref str hi)))
  29.                (string-set! str hi
  30.                  (fix-case (string-ref str hi) temp)))
  31.             (loop (+ lo 1) (- hi 1)))
  32.           ((not (vowel? (string-ref str lo))) (loop (+ lo 1) hi))
  33.           ((not (vowel? (string-ref str hi))) (loop lo (- hi 1)))
  34.           (else (loop (+ lo 1) (- hi 1))))))
  35.  
  36. (display (reverse-vowels "HELLO world")) (newline)
  37. (display (reverse-vowels "Programming PRAXIS")) (newline)
Success #stdin #stdout 0.02s 50288KB
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HOLLO werld
Prigramming PRAXOS
HOLLO werld
Prigramming PRAXOS
https://ideone.com/12nlr2
language:
Scheme (guile 2.2.4)
created:
4 years ago
visibility:
public

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