Benny, thanks for your explanation. It does make sense and clarifies
the issue. What DOES NOT make sense is
Clojure 1.2.0
user=> (conj (conj (conj #{4} 3) 2) 1)
#{1 2 3 4}
user=> (conj (conj (conj #{6857} 1471) 839) 71)
#{71 839 6857 1471}
Any ideas?
On Jan 13, 11:36 am, 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 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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