https://www.hackerrank.com/challenges/plus-minus

plusminus.clj

#!/usr/bin/env boot

(require '[clojure.string :as string])

(defn- str->int [s]
  (Integer/parseInt s))

(defn- positive? [n]
  (> n 0))

(defn- negative? [n]
  (< n 0))

(defn- format-float [f]
  (format "%.6f" (float f)))

(defn- filter-count [predicate collection]
  (count (filter predicate collection)))

(defn -main [& args]
  (let [expected-count (str->int (read-line))
        nums (map str->int (string/split (read-line) #"\s+"))
        actual-count (count nums)]
    (assert (= expected-count actual-count)
            (format "expected a collection of %d numbers, got %d" expected-count actual-count))
    (println (format-float (/ (filter-count positive? nums) actual-count)))
    (println (format-float (/ (filter-count negative? nums) actual-count)))
    (println (format-float (/ (filter-count zero? nums) actual-count)))))