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  1. ; move spaces to front
  2.  
  3. (define (spaces-to-front str)
  4.   (define (swap! a b)
  5.     (let ((temp (string-ref str a)))
  6.       (string-set! str a (string-ref str b))
  7.       (string-set! str b temp)))
  8.   (let ((len (- (string-length str) 1)))
  9.     (let loop ((i len) (j len))
  10.       (cond ((negative? i)
  11.               (do ((j j (- j 1)))
  12.                   ((negative? j) str)
  13.                 (string-set! str j #\space)))
  14.             ((char=? #\space (string-ref str i))
  15.               (loop (- i 1) j))
  16.             (else (swap! i j) (loop (- i 1) (- j 1)))))))
  17.  
  18. (display (spaces-to-front "h e l l o")) (newline)
  19. (display (spaces-to-front "hello    ")) (newline)
  20. (display (spaces-to-front "    hello")) (newline)
  21.  
  22. (define (spaces-to-front str)
  23.   (define (swap! a b)
  24.     (let ((temp (string-ref str a)))
  25.       (string-set! str a (string-ref str b))
  26.       (string-set! str b temp)))
  27.   (set! str (string-append str (string #\nul)))
  28.   (let loop ((i 0) (j 0))
  29.     (cond ((char=? (string-ref str j) #\nul) str)
  30.           ((char=? (string-ref str j) #\space)
  31.             (swap! i j) (loop (+ i 1) (+ j 1)))
  32.           (else (loop i (+ j 1))))))
  33.  
  34. (display (spaces-to-front "h e l l o")) (newline)
  35. (display (spaces-to-front "hello    ")) (newline)
  36. (display (spaces-to-front "    hello")) (newline)
Success #stdin #stdout 0s 42848KB
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Standard input is empty
stdout
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    hello
    hello
    hello
    lelho
    ohell
    hello
https://ideone.com/FECXsR
language:
Scheme (guile 2.2.4)
created:
6 years ago
visibility:
public

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