Interpreting a benchmark in C, Clojure, Python, Ruby, Scala and others [closed]

Answer 1

Here's a fast Clojure version, using the same basic algorithms:

(set! *unchecked-math* true)

(defn is-prime? [^long n]
  (loop [i 2]
    (if (zero? (unchecked-remainder-int n i))
      false
      (if (>= (inc i) n)
        true
        (recur (inc i))))))

(defn sexy-primes [m]
  (for [x (range 11 (inc m))
        :when (and (is-prime? x) (is-prime? (- x 6)))]
    [(- x 6) x]))

It runs about 20x faster than your original on my machine. And here's a version that leverages the new reducers library in 1.5 (requires Java 7 or JSR 166):

(require '[clojure.core.reducers :as r]) ;'

(defn sexy-primes [m]
  (->> (vec (range 11 (inc m)))
       (r/filter #(and (is-prime? %) (is-prime? (- % 6))))
       (r/map #(list (- % 6) %))
       (r/fold (fn ([] []) ([a b] (into a b))) conj)))

This runs about 40x faster than your original. On my machine, that's 100k in 1.5 seconds.