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  1. (set! *unchecked-math* true)
  2.  
  3. (defn grep-n-chunk [^long n f coll]
  4.   (lazy-seq
  5.    (when-let [s (seq coll)]
  6.      (if (and (chunked-seq? coll) (> (count (chunk-first coll)) (+ 1 (* 2 n)))) ;; :(
  7.        (let [fchunk (chunk-first coll)
  8.              c (count fchunk)
  9.              pred (chunk-buffer n)
  10.              matches (chunk-buffer c)
  11.              after (chunk-buffer n)]
  12.          (loop [i 0 last-match-idx nil]
  13.            (if (< i c)
  14.              (let [x (nth fchunk i)]
  15.                (if (and last-match-idx (<= i (+ n last-match-idx)))
  16.                  (do (chunk-append after x) (recur (inc i) last-match-idx))
  17.                  (if (f x)
  18.                    (do (chunk-append matches x)
  19.                        (dotimes [step n]
  20.                          (let [pred-match (nth fchunk (dec (- i step)) ::nil)]
  21.                            (when (not= pred-match ::nil)
  22.                              (chunk-append pred pred-match))))
  23.                        (recur (inc i) i))
  24.                    (recur (inc i) last-match-idx))))))
  25.          (->> (grep-n-chunk n f (chunk-rest coll))
  26.               (chunk-cons (chunk after))
  27.               (chunk-cons (chunk matches))
  28.               (chunk-cons (chunk pred))))
  29.        (let [p (take-while (complement f) (take n s))
  30.              n-till-first-match (count p)
  31.              matches (take-while f (nthrest s n-till-first-match))]
  32.          (if (seq matches)
  33.            (let [n-till-last-match (+ (count p) (count matches))
  34.                  a (take n (nthrest s n-till-last-match))]
  35.              (if (some f a)
  36.                (concat p matches (grep-n-chunk n f (nthrest s n-till-last-match)))
  37.                (concat p matches a (grep-n-chunk n f (nthrest s (+ n-till-last-match (count a)))))))
  38.            (grep-n-chunk n f (rest s))))))))
  39.  
  40.  
  41. (defn sample [] (doall (grep-n-chunk 2 #(.get #{1 1111 1111111} %) (range 100000000))))
  42. (time (sample))
Success #stdin #stdout 4.98s 128076KB
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Standard input is empty
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"Elapsed time: 3822.715114 msecs"
https://ideone.com/kLp0pH
language:
Clojure (clojure 1.10.0)
created:
6 years ago
visibility:
secret

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