用clojure解决 euler problem 2

问题描述:

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...

By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.

解决方案:

(ns euler-problem-2.core)
(defn fibonacci-even-sum 
  [max-num]
  (loop
      [n1 1, n2 2, sum 0]
    (if (< n1  max-num)
       (if (even? n1)
         (recur n2 (+ n1 n2) (+ sum n1))
         (recur n2 (+ n1 n2)  sum) )
       sum )))
(fibonacci-even-sum 4000000)

"Elapsed time: 0.201702 msecs"