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(ns tw.weekly.c106.t2
(:require [clojure.edn :as edn]
[clojure.math.numeric-tower :refer [abs]]))
;;;
; Task description for TASK #2 › Decimal String
;;;
(def DEFAULT-INPUT [1 3])
(defn- decimal-string-recurring
"Covert the given n[umerator] and d[enominator] (which must be known to
have a recurring fractional result) into a decimal string where the recurring
fractional is put in parenthesis."
[n d]
(loop [remainder (abs (rem n d))
cache {}
result []]
(if (not (or (zero? remainder) (cache remainder)))
(recur (rem (* 10 remainder) d)
(assoc cache remainder (count (apply str result)))
(conj result (quot (* 10 remainder) d)))
(let [[lead recurrence] (->> result (split-at (get cache remainder 0)))
whole (quot n d)
pieces (concat [whole \.] lead [\(] recurrence [\)])]
(apply str pieces)))))
(defn decimal-string
"Covert the given n[umerator] and d[enominator] into a decimal string where any
recurring fractional is put in parenthesis."
[n d]
(try (str (/ (bigdec n) d))
(catch ArithmeticException _
; BigDecimal throws this exception when the result cannot be
; represented with the 'UNLIMITED' precision (the default), i.e.,
; there is a recurring fractional result
(decimal-string-recurring n d))))
(defn -main
"Run Task 2 with a given N and D, defaulting to the example given in the task
description."
[& args]
(let [[N D] (or (some->> args (take 2) (map edn/read-string)) DEFAULT-INPUT)]
(println (decimal-string N D))))
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