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Run-length encoding: Difference between revisions
adding scheme
(→{{header|Pascal}}: add example) |
(adding scheme) |
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To make it faster (it's also faster than the longer implementation above) just replace '''""''' with '''new StringBuilder''' and '''s+i+p''' with '''{s.append(i);s.append(p)}'''
=={{header|Scheme}}==
<lang scheme>(define (run-length-decode v)
(apply string-append (map (lambda (p) (make-string (car p) (cdr p))) v)))
(define (run-length-encode s)
(let ((n (string-length s)))
(let loop ((n (- n 2)) (c (string-ref s (- n 1))) (k 1) (v '()))
(if (negative? n) (cons (cons k c) v)
(let ((x (string-ref s n)))
(if (char=? c x) (loop (- n 1) c (+ k 1) v)
(loop (- n 1) x 1 (cons (cons k c) v))))))))
(run-length-encode "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW")
; ((12 . #\W) (1 . #\B) (12 . #\W) (3 . #\B) (24 . #\W) (1 . #\B) (14 . #\W))
(run-length-decode '((12 . #\W) (1 . #\B) (12 . #\W) (3 . #\B) (24 . #\W) (1 . #\B) (14 . #\W)))
; "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"</scheme>
=={{header|sed}}==
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