Run-length encoding: Difference between revisions
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(→{{header|J}}: simplify and speed up rle) |
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'''Final note''': since the repeat counter value 0 has no meaning, it could be used as it would be 256, so extending by one the maximum number of repetitions representable with a single byte; or instead it could be used as a special marker to encode in a more efficient way (long) sequences of ''isolated characters'', e.g. "ABCDE" would be encoded as "1A1B1C1D1E"; it could be instead encoded as "05ABCDE". |
'''Final note''': since the repeat counter value 0 has no meaning, it could be used as it would be 256, so extending by one the maximum number of repetitions representable with a single byte; or instead it could be used as a special marker to encode in a more efficient way (long) sequences of ''isolated characters'', e.g. "ABCDE" would be encoded as "1A1B1C1D1E"; it could be instead encoded as "05ABCDE". |
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=={{header|Clojure}}== |
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<lang clojure> |
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(defn step [[result, n, c], new] ;function used in encode's reduce call |
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(cond |
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(zero? n) [result, 1, new] |
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(= c new) [result, (inc n), c] |
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:else [(conj result [n c]), 1, new])) |
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(defn encode [s] |
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(let [[result,n,chr] (reduce step [[],0,nil] s)] |
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(if (= n 0) |
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result |
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(conj result [n chr])))) |
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(defn decode [v] |
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(let [expand (fn [[n c]] (repeat n c))] |
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(apply str (mapcat expand v)))) |
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</lang> |
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<lang clojure> |
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(def uncoded "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW") |
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(def coded [[12 \W] [1 \B] [12 \W] [3 \B] [24 \W] [1 \B] [14 \W]]) |
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(assert (= (encode uncoded) coded)) |
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(assert (= (decode coded) uncoded)) |
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</lang> |
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=={{header|Common Lisp}}== |
=={{header|Common Lisp}}== |
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