fsharp-learning/exercism/fsharp/grains

Grains

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, with the number of grains doubling on each successive square.

There are 64 squares on a chessboard (where square 1 has one grain, square 2 has two grains, and so on).

Write code that shows:

• how many grains were on a given square, and
• the total number of grains on the chessboard

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?

Hints

For this exercise the following F# features come in handy:

• BigInt
• Seq.sumBy is a condensed format to apply a function to a sequence and then sum the results

Running the tests

To run the tests, run the command dotnet test from within the exercise directory.

Autoformatting the code

F# source code can be formatted with the Fantomas tool.

After installing it with dotnet tool restore, run dotnet fantomas . to format code within the current directory.

Further information

For more detailed information about the F# track, including how to get help if you’re having trouble, please visit the exercism.io F# language page.

Source

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