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Published at Jan 28 2021
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Instructions

Test suite

Solution

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

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?

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

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

```
(ns grains-test
(:require [clojure.test :refer [deftest is]]
grains))
(deftest square-1
(is (= 1 (grains/square 1))))
(deftest square-2
(is (= 2 (grains/square 2))))
(deftest square-3
(is (= 4 (grains/square 3))))
(deftest square-4
(is (= 8 (grains/square 4))))
(deftest square-16
(is (= 32768 (grains/square 16))))
(deftest square-32
(is (= 2147483648 (grains/square 32))))
(deftest square-64
(is (= 9223372036854775808 (grains/square 64))))
(deftest total-grains
(is (= 18446744073709551615 (grains/total))))
```

```
(ns grains)
(defn- expo [base exponent]
(if (zero? exponent)
1
(->> (bigint base)
(repeat exponent)
(apply *))))
(defn square [n]
(expo 2 (dec n)))
(defn total []
(dec (square 65)))
```

A huge amount can be learned from reading other peopleâ€™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?

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