coin_toss.clj

(ns coin-toss
  (:require [clojure.test :as t]))


(defn expt
  "x to the yth power" [x y]
  (apply * (repeat y x)))

(defn sum-of-geometric-series
  "a(1-r^n )/(1-r)" [a r n]
  (* a (/ (- 1 (expt r n)) (- 1 r))))


(t/deftest sum-of-geometric-series-test
  (t/testing "geometric series with a=1/6, r=5/6 and n=4 should equal 1- ((5/6) ^ 4)"
    (t/is (= (coin-toss/sum-of-geometric-series 1/6 5/6 4) (- 1 (coin-toss/expt 5/6 4))))
    (t/is (= (coin-toss/sum-of-geometric-series 1/36 35/36 24) (- 1 (coin-toss/expt 35/36 24))))))