http://codegolf.stackexchange.com/questions/18474/create-a-programs-that-counts-the-0s-in-numbers-from-0-to-a-billion

countzeros.clj

(defn numofzeros
  "Returns number of zeros in a number. Eg, 1000 returns 3."
  [input]
  (count (filter #(= \0 %) (str input))))

(defn countall
  "Count all number of zeros contained in all numbers between 0 and n (inclusive)
  Returns map of number of zeros in n and sum of all combined zeros"
  [n]
  (let [lastnumzeros (numofzeros n)
    sum (reduce (fn [acc x] (+ acc (numofzeros x))) 0 (range (inc n)))]
    {:zeros lastnumzeros :sum sum}))

(println (countall (long 1e9))