Solutions to 3 Project Euler problems for Clojure 101 at 8th Light.

euler.clj

(ns euler.core)

(defn multiple-of-3-or-5? [n] (or (= 0 (mod n 3)) (= 0 (mod n 5))))

(defn sum-of-multiples-of-3-or-5-below [n]
  (apply + (filter multiple-of-3-or-5? (range 1 n))))

(defn fibs []
  (map first (iterate (fn [[a b]] [b (+ a b)]) [1N 1N])))

(defn sum-of-even-fibonaccis-less-than [n]
  (apply + (filter even? (take-while #(< % n) (fibs)))))

(defn first-fibonacci-term-of-length-digits [n]
  ; (first (drop-while #(< (count (str %)) n) (fibs))))
  (let [[shorter-terms longer-terms] (split-with #(< (count (str %)) n) (fibs))]
    (+ 1 (count shorter-terms))))

euler_spec.clj

(ns euler.core-spec
  (:require [speclj.core :refer :all]
            [euler.core :refer :all]))

(describe "sum of multiples of 3 and 5 below 1000"
  (it "is 233168"
    (should= 233168 (sum-of-multiples-of-3-or-5-below 1000))))

(describe "sum of even Fibonacci numbers less than 4 million"
  (it "is 4613732"
    (should= 4613732 (sum-of-even-fibonaccis-less-than 4000000))))

(describe "first Fibonacci term of length digits"
  (it "is 4782"
    (should= 4782 (first-fibonacci-term-of-length-digits 1000))))-