hussainweb's solution to Grains on the Go track

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.
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?

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"
)

// Square returns the number of grains on a specific square
// of a chess-board
func Square(square int) (uint64, error) {
	if square <= 0 || square > 64 {
		return 0, errors.New("Invalid size")
	}

	// Same as 2 ^ (square - 1)
	return 1 << (square - 1), nil
}

// Total returns the number of grains for a chess-board
func Total() uint64 {
	return 1<<64 - 1
}

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hussainweb's solution

to Grains in the Go Track