2015-02-18 18:25 GMT+01:00 Cecil Westerhof <cldwester...@gmail.com>:
> 2015-02-18 16:31 GMT+01:00 Tassilo Horn <t...@gnu.org>:
>
>> Here's my version:
>>
>> --8<---------------cut here---------------start------------->8---
>> (defn drop-every-nth [c n]
>> (keep-indexed (fn [i el]
>> (if (zero? (mod (inc i) n)) nil el))
>> c))
>>
>> (defn lucky-numbers [n]
>> (loop [c (range 1 (inc n) 2), survivor-idx 1]
>> (let [i (nth c survivor-idx)]
>> (if (> (count c) i)
>> (recur (drop-every-nth c i) (inc survivor-idx))
>> c))))
>> --8<---------------cut here---------------end--------------->8---
>>
>
> By the way: it goes wrong for values below 3.
>
This way it works OK:
(defn lucky-numbers
"Lucky numbers from 1 up-to upto-value.
1 <= upto-value <= 10.000.000
http://en.wikipedia.org/wiki/Lucky_number";
; doc-string and pre-condition should match
[upto]
{:pre [(>= upto 1)
(<= upto (* 10 1000 1000))]}
(if (< upto 3)
(list 1)
(loop [coll (range 1 (inc upto) 2), survivor-idx 1]
(let [i (nth coll survivor-idx)]
(if (> (count coll) i)
(recur (drop-every-nth coll i) (inc survivor-idx))
coll)))))
I discovered pre-conditions. Makes the code a lot clearer. (I still work
with a maximum value.)
--
Cecil Westerhof
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