Exercism v3 launches on Sept 1st 2021. Learn more! ðŸš€ðŸš€ðŸš€

Published at Jun 02 2020
·
0 comments

Instructions

Test suite

Solution

Find the difference between the square of the sum and the sum of the squares of the first N natural numbers.

The square of the sum of the first ten natural numbers is (1 + 2 + ... + 10)Â² = 55Â² = 3025.

The sum of the squares of the first ten natural numbers is 1Â² + 2Â² + ... + 10Â² = 385.

Hence the difference between the square of the sum of the first ten natural numbers and the sum of the squares of the first ten natural numbers is 3025 - 385 = 2640.

You are not expected to discover an efficient solution to this yourself from first principles; research is allowed, indeed, encouraged. Finding the best algorithm for the problem is a key skill in software engineering.

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

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.

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.

Problem 6 at Project Euler http://projecteuler.net/problem=6

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

```
package diffsquares
import "testing"
var tests = []struct{ n, sqOfSum, sumOfSq int }{
{5, 225, 55},
{10, 3025, 385},
{100, 25502500, 338350},
}
func TestSquareOfSum(t *testing.T) {
for _, test := range tests {
if s := SquareOfSum(test.n); s != test.sqOfSum {
t.Fatalf("SquareOfSum(%d) = %d, want %d", test.n, s, test.sqOfSum)
}
}
}
func TestSumOfSquares(t *testing.T) {
for _, test := range tests {
if s := SumOfSquares(test.n); s != test.sumOfSq {
t.Fatalf("SumOfSquares(%d) = %d, want %d", test.n, s, test.sumOfSq)
}
}
}
func TestDifference(t *testing.T) {
for _, test := range tests {
want := test.sqOfSum - test.sumOfSq
if s := Difference(test.n); s != want {
t.Fatalf("Difference(%d) = %d, want %d", test.n, s, want)
}
}
}
// Benchmark functions on just a single number (100, from the original PE problem)
// to avoid overhead of iterating over tests.
func BenchmarkSquareOfSum(b *testing.B) {
for i := 0; i < b.N; i++ {
SquareOfSum(100)
}
}
func BenchmarkSumOfSquares(b *testing.B) {
for i := 0; i < b.N; i++ {
SumOfSquares(100)
}
}
func BenchmarkDifference(b *testing.B) {
for i := 0; i < b.N; i++ {
Difference(100)
}
}
```

```
package diffsquares
// SquareOfSum returns (1 + 2 + ... + n) ^ 2
func SquareOfSum(n int) int {
sum := 0
for i := 0; i <= n; i++ {
sum += i
}
return sum * sum
}
// SumOfSquares returns 1^2 + 2^2 + ... + n^2
func SumOfSquares(n int) int {
sum := 0
for i := 0; i <= n; i++ {
sum += i * i
}
return sum
}
// Difference returns the difference between the SquareOfSum(n) and SumOfSquares(n)
func Difference(n int) int {
return SquareOfSum(n) - SumOfSquares(n)
}
```

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?

Level up your programming skills with 3,450 exercises across 52 languages, and insightful discussion with our volunteer team of welcoming mentors.
Exercism is
**100% free forever**.

## Community comments