What is the first term in the Fibonacci sequence to contain 1000 digits?
We've introduced Fibonacci sequence at Clojure Euler: Problem 002
Lazy sequence generates fibonacci numbers is dead simple:
(defn fibonacci  (->> [0 1] (iterate (fn [[a b]] [b (+' a b)])) (map first)))
We also can count the length of number in digits. No decimal arithmetic. Cast number to string, and take length of a string
(defn num-of-digits [n] (count (str n)))
To solve the problem use the most straightforward approach and you'll find the answer in less than 1 second.
(->> (fibonacci) (map-indexed (fn [i n] [i (num-of-digits n)])) (drop-while #(< (second %) 1000)) (first) (first))
P.S. If you followed all posts upto this one, then you have 25 problems solved, level 1 and nice badge
mishadoff 09 September 2014