🎉 Exercism Research is now launched. Help Exercism, help science and have some fun at research.exercism.io 🎉
Avatar of n0mn0m

n0mn0m's solution

to Grains in the Racket Track

Published at Nov 14 2020 · 0 comments
Test suite

Calculate the number of grains of wheat on a chessboard given that the number on each square doubles.

There once was a wise servant who saved the life of a prince. The king promised to pay whatever the servant could dream up. Knowing that the king loved chess, the servant told the king he would like to have grains of wheat. One grain on the first square of a chess board. Two grains on the next. Four on the third, and so on.

There are 64 squares on a chessboard.

Write code that shows:

  • how many grains were on each square, and
  • the total number of grains

For bonus points

Did you get the tests passing and the code clean? If you want to, these are some additional things you could try:

  • Optimize for speed.
  • Optimize for readability.

Then please share your thoughts in a comment on the submission. Did this experiment make the code better? Worse? Did you learn anything from it?

For installation and learning resources, refer to the exercism Racket page.

You can run the provided tests through DrRacket, or via the command line.

To run the test through DrRacket, simply open the test file and click the 'Run' button in the upper right.

To run the test from the command line, run the test from the exercise directory with the following command:

raco test grains-test.rkt

which will display the following:

raco test: (submod "grains-test.rkt" test)
2 success(es) 0 failure(s) 0 error(s) 2 test(s) run
2 tests passed


JavaRanch Cattle Drive, exercise 6 http://www.javaranch.com/grains.jsp

Submitting Incomplete Solutions

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


#lang racket/base

(require "grains.rkt")

(module+ test
  (require rackunit rackunit/text-ui)

  (define suite
     "grains tests"

     (test-eqv? "square 1" (square 1) 1)
     (test-eqv? "square 2" (square 2) 2)
     (test-eqv? "square 3" (square 3) 4)
     (test-eqv? "square 4" (square 4) 8)
     (test-eqv? "square 16" (square 16) 32768)
     (test-eqv? "square 32" (square 32) 2147483648)
     (test-eqv? "square 64" (square 64) 9223372036854775808)
     (test-eqv? "total grains" (total) 18446744073709551615)))

  (run-tests suite))
#lang racket

(provide square total)

(define (square n)
  (expt 2 (- n 1)))

(define (total) (- (square 65) 1))

Community comments

Find this solution interesting? Ask the author a question to learn more.

What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
  • Are there new concepts here that you could read more about to improve your understanding?