Bits and Bikes

Ideas, digital, analog, and pedal-driven.

A Proper Solution to Project Euler Problem Sixteen

Here's my solution to Project Euler problem sixteen, written in Clojure. I'm a bit offended by most of the solutions in the message thread because they require bignum support, which is basically a pathetically easy way to solve this problem.

(defn carry [coll]
    (reverse
     (loop [c coll extra 0 acc '()]
       (if (nil? c)
         (if (zero? extra) acc (cons 1 acc))
         (let [v (+ extra (first c))]
           (recur (next c) (int (/ v 10)) (cons (mod v 10) acc)))))))
  
  (defn dbl [coll]
    (carry (map (partial * 2) coll)))

  (defn eul-16 [iters]
    (reduce + 0
            (loop [n 0 acc '(1)]
              (if (= n iters)
                acc
                (recur (inc n) (dbl acc))))))

  (eul-16 1000)