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# epequeno's solution

## to Grains in the Rust Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

#### Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

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.

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?

## Rust Installation

Refer to the exercism help page for Rust installation and learning resources.

## Writing the Code

Execute the tests with:

``````\$ cargo test
``````

All but the first test have been ignored. After you get the first test to pass, open the tests source file wich is located in the `tests` directory and remove the `#[ignore]` flag from the next test and get the tests to pass again. Each separate test is a function with `#[test]` flag above it. Continue, until you pass every test.

If you wish to run all tests without editing the tests source file, use:

``````\$ cargo test -- --ignored
``````

To run a specific test, for example `some_test`, you can use:

``````\$ cargo test some_test
``````

If the specfic test is ignored use:

``````\$ cargo test some_test -- --ignored
``````

## Feedback, Issues, Pull Requests

The exercism/rust repository on GitHub is the home for all of the Rust exercises. If you have feedback about an exercise, or want to help implement new exercises, head over there and create an issue. Members of the rust track team are happy to help!

If you want to know more about Exercism, take a look at the contribution guide.

## Source

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.

### grains.rs

``````extern crate grains;

#[test]
fn square_one() {
assert_eq!(grains::square(1), 1);
}

#[test]
#[ignore]
fn square_two() {
assert_eq!(grains::square(2), 2);
}

#[test]
#[ignore]
fn square_three() {
assert_eq!(grains::square(3), 4);
}

#[test]
#[ignore]
fn square_four() {
assert_eq!(grains::square(4), 8);
}

#[test]
#[ignore]
fn square_sixteen() {
assert_eq!(grains::square(16), 32_768);
}

#[test]
#[ignore]
fn square_thirty_two() {
assert_eq!(grains::square(32), 2_147_483_648);
}

#[test]
#[ignore]
fn square_sixty_four() {
assert_eq!(grains::square(64), 9_223_372_036_854_775_808);
}

#[test]
#[ignore]
#[should_panic(expected = "Square must be between 1 and 64")]
fn square_zero_panics() {
grains::square(0);
}

#[test]
#[ignore]
#[should_panic(expected = "Square must be between 1 and 64")]
fn square_sixty_five_panics() {
grains::square(65);
}

#[test]
#[ignore]
fn total_sums_all_squares() {
assert_eq!(grains::total(), 18_446_744_073_709_551_615);
}``````
``````pub fn square(s: u32) -> u64 {
if s < 1 || s > 64 {
panic!("Square must be between 1 and 64");
}
2u64.pow(s-1)
}

pub fn total() -> u64 {
let mut total = 0;
for i in 1..65 {
total += square(i);
}
total
}``````