Prime Factors Kata

August 03, 2021

I did my first kata yesterday and recorded it, the prime factors kata in Clojure. The idea behind a kata is to practice your programming craft, it’s not about the final code but about the dicipline.

I’ve done it a few times already, each time I do it I feel more comfortable. Today I learned about loop and recursion in Clojure.

Repetition is the mother of mastery.

I followed Uncle bob steps, and worked my way up the test cases until my code magically was supporting all numbers!

I found it interesting that we don’t test cases 5 and 7, it seems Uncle Bob is telling us we don’t need them as if we follow the steps these cases get resolved on the generate prime factors method.

Youtube

(ns prime-factors-kata.core)
(defn generate [n]
  (loop [n n
         [accum possible-divider] [ [] 2 ]]
    (if (<= n 1)
      accum
      (if (<= n 3)
        (conj accum n)
        (if (= 0 (mod n possible-divider))
          (recur (/ n possible-divider) [(conj accum possible-divider) 2])
          (recur n [accum (inc possible-divider)])))))

Tests:

(ns prime-factors-kata.core-spec
  (:require [speclj.core :refer :all]
            [prime-factors-kata.core :refer :all]))
(describe "Prime factors generator"
  (it "returns an empty list when n is 1"
    (should= [] (generate 1)))
  (it "returns an [2] when n is 2"
    (should= [2] (generate 2)))
  (it "returns an [3] when n is 3"
    (should= [3] (generate 3)))
  (it "returns an [2 2] when n is 4"
    (should= [2 2] (generate 4)))
  (it "returns an [2 3] when n is 6"
    (should= [2 3] (generate 6)))
  (it "returns an [2 2 2] when n is 8"
    (should= [2 2 2] (generate 8)))
  (it "returns an [3 3] when n is 9"
    (should= [3 3] (generate 9)))
  (it "doesn't blow the stack"
    (should= [2 2 3 3 5 5] (generate 900))))

Written by Edgardo Carreras.

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