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Last active Feb 13, 2017
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(defn digits [x]
(loop [r x, digits []]
(if (== 0 r)
(recur (quot r 10) (conj digits (rem r 10))))))
(defn double-odd-digits [digits]
(map-indexed (fn [i d] (if (odd? i) (* 2 d) d)) digits))
(defn valid? [x]
(let [sum (->> (digits x)
(mapcat digits)
(reduce + 0))]
(== 0 (rem sum 10))))
(use 'clojure.test)
(is (valid? 4012888888881881))
(is (not (valid? 4012888888881882)))
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