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snt/luhn-check-digit.clj

Created November 28, 2013 08:45
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luhn-check-digit.clj
(defn luhn-check-digit [numStr]
(let [char-to-integer (fn [c] (Integer/parseInt (str c)))
prod-tuple (fn [t] (* (t 0) (t 1)))
sum-digits (fn [n] (if (> n 9) (- n 9) n))]
(->> numStr
reverse
(map char-to-integer)
(zip (cycle [2 1]))
(map (comp sum-digits prod-tuple))
(reduce +)
(#(mod % 10))
(- 10))))
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