37 lines
1.3 KiB
Clojure
37 lines
1.3 KiB
Clojure
(use 'clojure.contrib.seq-utils)
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(defn probs [items]
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(let [freqs (frequencies items) sum (reduce + (vals freqs))]
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(into {} (map (fn [[k v]] [k (/ v sum)]) freqs))))
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(defn init-pq [weighted-items]
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(let [comp (proxy [java.util.Comparator] []
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(compare [a b] (compare (:priority a) (:priority b))))
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pq (java.util.PriorityQueue. (count weighted-items) comp)]
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(doseq [[item prob] weighted-items] (.add pq { :symbol item, :priority prob }))
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pq))
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(defn huffman-tree [pq]
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(while (> (.size pq) 1)
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(let [a (.poll pq) b (.poll pq) new-node { :priority (+ (:priority a) (:priority b)), :left a, :right b }]
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(.add pq new-node)))
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(.poll pq))
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(defn symbol-map
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([t] (into {} (symbol-map t [])))
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([{:keys [symbol,left,right] :as t} code]
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(if symbol [[symbol code]]
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(concat (symbol-map left (conj code 0))
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(symbol-map right (conj code 1))))))
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(defn huffman-encode [items]
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(-> items probs init-pq huffman-tree symbol-map))
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(defn display-huffman-encode [s]
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(println "SYMBOL\tWEIGHT\tHUFFMAN CODE")
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(let [probs (probs (seq s))]
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(doseq [[char code] (huffman-encode (seq s))]
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(printf "%s:\t\t%s\t\t%s\n" char (probs char) (apply str code)))))
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(display-huffman-encode "this is an example for huffman encoding")
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