Fast prime sort algorithm

problem07.clj

(ns euler.problem7
  (:use [euler.core]))

;; The algorithm for this is
;; - Start at the first 1000 primes
;; - If there are not enough primes then try again at 2000 etc

(defn get-nth-prime [n, max]
  "Returns the nth prime"
  (let [primes (sieve max)]
    (if (< (count primes) n)
      (recur  n (* max 2))
      (last (take n primes)))))

(defn solve [n]
  (get-nth-prime n 1000))

(time (solve 10000))

;; "Elapsed time: 149.609 msecs"
;; 104729