2015-02-19 23:25 GMT+01:00 Steve Miner <[email protected]>:
> I found a better data structure for calculating lucky numbers. The
> contrib library data.avl (from Michał Marczyk) has a persistent sorted-set
> that supports nth. This runs much faster than my previous attempts.
>
> (require '[clojure.data.avl :as avl])
>
> (defn lucky-avl
> ([max] (lucky-avl 1 (apply avl/sorted-set (range 1 max 2))))
> ([i avl]
> (let [n (nth avl i nil)]
> (if (and n (<= n (count avl)))
> (recur (inc i) (reduce (fn [sss m] (disj sss (nth avl m)))
> avl
> (range (dec n) (count avl) n)))
> (sequence avl)))))
>
> (time (count (lucky-avl 1e6)))
> "Elapsed time: 2396.158435 msecs"
> 71918
>
It works especially well for bigger values. With 1e7 I got with the old
version:
"Elapsed time: 3924244.877112 msecs"
and with this version:
"Elapsed time: 14863.904489 msecs"
More as 250 times as fast.
--
Cecil Westerhof
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