On Thu, Jan 13, 2011 at 17:36, Benny Tsai <benny.t...@gmail.com> wrote:
> (conj) will add items to different places in the collection, depending
> on the type of the collection. For a set, this can be at either the
> end OR the beginning.
For a (hashed) set, this can be *anywhere* (between existing elements too).
FTFY
// Ben
> For this problem, the output is built by:
>
> (conj (conj (conj #{6857} 1471) 839) 71)
>
> which is equivalent to:
>
> (-> #{6857} (conj 1471) (conj 839) (conj 71))
>
> The innermost/first conj, (conj #{6857} 1471), sticks 1471 at the end
> and produces #{6857 1471}. The next conj sticks 839 at the beginning
> and produces #{839 6857 1471}. The final conj sticks 71 at the
> beginning and produces the final result of #{71 839 6857 1471}.
>
> When ordering matters, I usually use either (cons), which will always
> add to the beginning regardless of the collection type, or use (conj)
> with a list (will always add to the beginning) or vector (will always
> add to the end).
>
> user=> (-> '(6857) (conj 1471) (conj 839) (conj 71))
> (71 839 1471 6857)
> user=> (-> [6857] (conj 1471) (conj 839) (conj 71))
> [6857 1471 839 71]
>
> On Jan 13, 8:09 am, Vitaly Peressada <vit...@ufairsoft.com> wrote:
>> The following solution by <b>mtgred</b> for <a href="http://clojure-
>> euler.wikispaces.com/">Project Euler Clojure</a> problem 003 uses
>> implicit recursion.
>>
>> <pre>
>> (use '[clojure.contrib.lazy-seqs :only (primes)])
>> (defn prime-factors [n]
>> (let [f (some #(if (= 0 (rem n %)) %) primes)]
>> (if (= f n) #{f} (conj (prime-factors (/ n f)) f))))
>> (apply max (prime-factors 600851475143))
>> </pre>
>>
>> Here is above with added println
>>
>> (defn prime-factors [n]
>> (let [f (some #(if (= 0 (rem n %)) %) primes)]
>> (println "n:" n ", f:" f)
>> (if (= f n)
>> #{f}
>> (conj (prime-factors (/ n f)) f))))
>>
>> Which produces
>>
>> n: 600851475143 , f: 71
>> n: 8462696833 , f: 839
>> n: 10086647 , f: 1471
>> n: 6857 , f: 6857
>> #{71 839 6857 1471}
>>
>> Can anybody explain why 6857 comes 3rd? I would expect to be the last.
>
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