gistfile1.clj

; This gist relates to Misophistful's video "Understanding list comprehension in Clojure"
; http://www.youtube.com/watch?v=5lvV9ICwaMo

(defn palindrome? [n]
  (let [s (str n)]
    (= s (clojure.string/reverse s))))

(def palindromes
  (for [n1 (range 100 1000)
        n2 (range 100 1000)
        :let [product (* n1 n2)]
        :when (palindrome? product)
    { :factors [n1 n2] :product product })    ; <--- generate a compound value for each palindrome

; This generates a sequence of maps:
; ( {:factors [101 101], :product 10201}
;   {:factors [101 111], :product 11211}
;   {:factors [101 121], :product 12221})
;   ...
;   )

; Now we can find the largest palindrome _and_ the numbers that made it.

(last (sort-by :product palindromes))
;= {:factors [993 913], :product 906609}