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Clojure – Project Euler Problem 4

by Vijay Kiran

This post is the part of the series Solving Project Euler’s problems with Clojure.

;; A palindromic number reads the same both ways. 
;; The largest palindrome made from the product of two 2-digit numbers is 9009 = 91  99.
;; Find the largest palindrome made from the product of two 3-digit numbers.
 
(:require '[clojure.string as :str])
(defn palindrome? 
  [n]
	(let [x (format "%d" n)]
		(= x (apply str (reverse x)))))
 
(println 
	(apply max (filter #(not (nil? %)) 
                              (distinct (for [i (range 999 99 -1) j (range 999 99 -1)] 
                        		(if (palindrome? (* i j)) (* i j)))))))

•

  • bonega

    I would do it like this:

    (defn palindrome? [n] (let [coll (seq (str n))]
    (= coll (reverse coll))))

    (->> (for [i (range 999 99 -1) j (range 999 99 -1)] (* i j))
    (filter palindrome?)
    (apply max))

    If only numbers were sequable :(