# rootulp's solution

## to Grains in the Go Track

Published at Jun 03 2020 · 0 comments
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, 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.

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?

## Coding the solution

Look for a stub file having the name grains.go and place your solution code in that file.

## Running the tests

To run the tests run the command `go test` from within the exercise directory.

If the test suite contains benchmarks, you can run these with the `--bench` and `--benchmem` flags:

``````go test -v --bench . --benchmem
``````

Keep in mind that each reviewer will run benchmarks on a different machine, with different specs, so the results from these benchmark tests may vary.

## Further information

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

## 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.

### cases_test.go

``````package grains

// Source: exercism/problem-specifications
// Commit: 2ec42ab Grains: Fixed canonical data to have standard error indicator (#1322)
// Problem Specifications Version: 1.2.0

// returns the number of grains on the square
var squareTests = []struct {
description string
input       int
expectedVal uint64
expectError bool
}{
{
description: "1",
input:       1,
expectedVal: 1,
},
{
description: "2",
input:       2,
expectedVal: 2,
},
{
description: "3",
input:       3,
expectedVal: 4,
},
{
description: "4",
input:       4,
expectedVal: 8,
},
{
description: "16",
input:       16,
expectedVal: 32768,
},
{
description: "32",
input:       32,
expectedVal: 2147483648,
},
{
description: "64",
input:       64,
expectedVal: 9223372036854775808,
},
{
description: "square 0 returns an error",
input:       0,
expectError: true,
},
{
description: "negative square returns an error",
input:       -1,
expectError: true,
},
{
description: "square greater than 64 returns an error",
input:       65,
expectError: true,
},
}``````

### grains_test.go

``````package grains

import (
"testing"
)

func TestSquare(t *testing.T) {
for _, test := range squareTests {
actualVal, actualErr := Square(test.input)

// check actualVal only if no error expected
if !test.expectError && actualVal != test.expectedVal {
t.Fatalf("FAIL: %s\nSquare(%d) expected %d, Actual %d", test.description, test.input, test.expectedVal, actualVal)
}

// if we expect an error and there isn't one
if test.expectError && actualErr == nil {
t.Fatalf("FAIL: %s\nSquare(%d) expected an error, but error is nil", test.description, test.input)
}
// if we don't expect an error and there is one
if !test.expectError && actualErr != nil {
var _ error = actualErr
t.Fatalf("FAIL: %s\nSquare(%d) expected no error, but error is: %s", test.description, test.input, actualErr)
}
t.Logf("PASS: %s", test.description)
}
}

func TestTotal(t *testing.T) {
var expected uint64 = 18446744073709551615
if actual := Total(); actual != expected {
t.Errorf("Total() expected %d, Actual %d", expected, actual)
}
}

func BenchmarkSquare(b *testing.B) {

for i := 0; i < b.N; i++ {

for _, test := range squareTests {
Square(test.input)
}

}
}

func BenchmarkTotal(b *testing.B) {
for i := 0; i < b.N; i++ {
Total()
}
}``````
``````package grains

import (
"errors"
"math"
)

// Square returns the number of grains on the provided square.
func Square(n int) (uint64, error) {
if n < 1 || n > 64 {
return 0, errors.New("square: n is not between 1 and 64 (inclusive)")
}
return uint64(math.Pow(2, float64(n-1))), nil
}

// Total returns the sum of all grains on the chess board.
func Total() uint64 {
var sum uint64 = 0
for i := 1; i <= 64; i++ {
var result, _ = Square(i)
sum += result
}
return sum
}``````