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shmibs's solution

to Raindrops in the OCaml Track

Published at Dec 08 2018 · 0 comments
Test suite


This exercise has changed since this solution was written.

Convert a number to a string, the contents of which depend on the number's factors.

  • If the number has 3 as a factor, output 'Pling'.
  • If the number has 5 as a factor, output 'Plang'.
  • If the number has 7 as a factor, output 'Plong'.
  • If the number does not have 3, 5, or 7 as a factor, just pass the number's digits straight through.


  • 28's factors are 1, 2, 4, 7, 14, 28.
    • In raindrop-speak, this would be a simple "Plong".
  • 30's factors are 1, 2, 3, 5, 6, 10, 15, 30.
    • In raindrop-speak, this would be a "PlingPlang".
  • 34 has four factors: 1, 2, 17, and 34.
    • In raindrop-speak, this would be "34".

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A variation on a famous interview question intended to weed out potential candidates. http://jumpstartlab.com

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.


open OUnit2
open Raindrops

let ae exp got _test_ctxt = assert_equal ~printer:(fun x -> x) exp got

let tests = [
   "the sound for 1 is 1" >::
      ae "1" (raindrop 1);
   "the sound for 3 is Pling" >::
      ae "Pling" (raindrop 3);
   "the sound for 5 is Plang" >::
      ae "Plang" (raindrop 5);
   "the sound for 7 is Plong" >::
      ae "Plong" (raindrop 7);
   "the sound for 6 is Pling as it has a factor 3" >::
      ae "Pling" (raindrop 6);
   "2 to the power 3 does not make a raindrop sound as 3 is the exponent not the base" >::
      ae "8" (raindrop 8);
   "the sound for 9 is Pling as it has a factor 3" >::
      ae "Pling" (raindrop 9);
   "the sound for 10 is Plang as it has a factor 5" >::
      ae "Plang" (raindrop 10);
   "the sound for 14 is Plong as it has a factor of 7" >::
      ae "Plong" (raindrop 14);
   "the sound for 15 is PlingPlang as it has factors 3 and 5" >::
      ae "PlingPlang" (raindrop 15);
   "the sound for 21 is PlingPlong as it has factors 3 and 7" >::
      ae "PlingPlong" (raindrop 21);
   "the sound for 25 is Plang as it has a factor 5" >::
      ae "Plang" (raindrop 25);
   "the sound for 27 is Pling as it has a factor 3" >::
      ae "Pling" (raindrop 27);
   "the sound for 35 is PlangPlong as it has factors 5 and 7" >::
      ae "PlangPlong" (raindrop 35);
   "the sound for 49 is Plong as it has a factor 7" >::
      ae "Plong" (raindrop 49);
   "the sound for 52 is 52" >::
      ae "52" (raindrop 52);
   "the sound for 105 is PlingPlangPlong as it has factors 3, 5 and 7" >::
      ae "PlingPlangPlong" (raindrop 105);
   "the sound for 3125 is Plang as it has a factor 5" >::
      ae "Plang" (raindrop 3125);

let () =
  run_test_tt_main ("raindrops tests" >::: tests)
open Core

let wordmap = [3, "Pling"; 5, "Plang"; 7, "Plong"]

let raindrop (i : int) =
  |> List.map ~f:(fun (k, v) -> if Int.rem i k = 0 then v else "")
  |> String.concat
  |> fun s -> if s = "" then (Int.to_string i) else s

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