| |
Exercise 1.21
| | (ns e1-21
(:use clojure.test))
Use the smallest-divisor procedure to find the smallest divisor of each of
the following numbers: 199, 1999, 19999.
| |
For it we'll need to implement the procedures described earlier in the
chapter.
| |
|
| | (defn divides? [a b]
(= (rem b a) 0))
|
| | (defn square [a]
(* a a))
|
| | (defn expmod [base exp m]
(cond (= exp 0) 1
(even? exp) (rem (square
(expmod base (/ exp 2) m)) m)
:else (rem (* base (expmod base (- exp 1) m))
m)))
|
| | (defn find-divisor [n test]
(cond (> (square test) n) n
(divides? test n) test
:else (find-divisor n (+ test 1))))
|
| | (defn smallest-divisor [n]
(find-divisor n 2))
|
| | (defn prime? [n]
(= (smallest-divisor n) n))
And the answer is...
| | (deftest test-smallest-divisor
(are [x y] (= (smallest-divisor x) y)
199 199
1999 1999
19999 7))
| | |