Thank you for the advice! Just for reference I am working on project
euler question #4 (Find the largest palindrome made from the product
of two 3-digit numbers.)
I have a solution, but am hoping somebody can clarify some things for
me:
First, I define a panlindrome tester:
(defn palindrome? [s]
(= s (apply str (reverse s))))
Next, I define a list of palindromes for the two 3-digit number range:
(def palindromes (filter #(palindrome? (str %)) (reverse (range (* 100
100) (+ 1 (* 999 999))))))
My next function takes a palindromic number as an argument and returns
a sequence of all 3 digit divisors with a 3 digit quotient
(defn divis-by-3dig [pal] (filter #(if (zero? (mod pal %)) (= 3 (len
(str (/ pal %))))) (reverse (range 100 1000))))
This function works, but only with an integer, which means I have to
use it with another filter function in order to test a collection.
And then it will return the palindromic number in my collection which
has two 3 digit divisors instead of the factors, which is what I am
looking for.
I solve this as follows in my main function:
(defn e1 []
(def palindromic-number (take 1 (filter #(not (empty? (divis-by-3dig
%))) palindromes)))
(def root (take 1 (map divis-by-3dig palindromic-number)))
root)
unfortunately there is still a problem with this, in that i cannot get
access to a single root, instead am returned all of the roots from
applying my divis-by-3dig function to the single element in my
collection palindromic-number
(e1)
On Feb 14, 8:52 am, "Steven E. Harris" <s...@panix.com> wrote:
> Glen Rubin <rubing...@gmail.com> writes:
> > How do I take an element from one collection and test for no remainder
> > (e.g. (zero? (mod x y)), when dividing by every element of the second
> > collection, before processing the next item in the first collection?
>
> This form checks if every element of the second range is a factor of
> every element in the first range:
>
> ,----
> | (let [r2 (range 100 150)]
> | (every?
> | #(every? (partial (comp zero? mod) %) r2)
> | (range 1000 2000)))
> `----
>
> Note that the walk over (range 1000 2000) is the outer one, and the walk
> over (range 100 150) ("r2") is the inner one.
>
> --
> Steven E. Harris
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