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  1. ; identifying palindromes
  2.  
  3. (define (palindrome? xv)
  4.   (let ((len (vector-length xv)))
  5.     (let loop ((left 0) (right (- len 1)))
  6.       (cond ((< right left) #t)
  7.             ((not (equal? (vector-ref xv left)
  8.                           (vector-ref xv right))) #f)
  9.             (else (loop (+ left 1) (- right 1)))))))
  10.  
  11. (display (palindrome? (vector 1 2 3 4 5 6 7))) (newline)
  12. (display (palindrome? (vector 1 2 3 4 3 2 1))) (newline)
  13.  
  14. (define (palindrome? xs)
  15.   (let loop ((h xs) (t xs) (front (list)))
  16.     (cond ((null? t) #t)
  17.           ((pair? h)
  18.             (if (pair? (cdr h))
  19.                 (loop (cddr h) (cdr t)
  20.                       (cons (car t) front))
  21.                 (loop (cdr h) (cdr t) front)))
  22.           ((equal? (car t) (car front))
  23.             (loop h (cdr t) (cdr front)))
  24.           (else #f))))
  25.  
  26. (display (palindrome? (list 1 2 3 4 5 6 7))) (newline)
  27. (display (palindrome? (list 1 2 3 4 3 2 1))) (newline)
Success #stdin #stdout 0s 7276KB
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https://ideone.com/22EEG0
language:
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created:
9 years ago
visibility:
public

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